FOUS30 KWBC 080815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
315 AM EST Mon Dec 8 2025

Day 1
Valid 12Z Mon Dec 08 2025 - 12Z Tue Dec 09 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

...Western Washington and Oregon...

The inherited Slight Risk across Western Washington and Oregon
remains little changed this morning. A hauling 150+ kt upper level
jet will bring a vigorous shortwave trough into British Columbia
north of the Canadian border Monday afternoon and evening. The
trailing front associated with the surface low that is being
strengthened by that shortwave will plow into the coast Monday
afternoon. Behind that disturbance, mid-level 850 mb flow will
rapidly increase out of the due west at at least 50 kt, while PWATs
also rapidly increase from 0.75 inches to 1.25 inches as the head
of the incoming atmospheric river (A.R.) makes its way ashore. On
the synoptic scale, the overall rainfall footprint will be greatest
today as compared with the expected rainfall over the next few
days. This in turn will set the stage for multiple days of flooding
concerns as the rain continues through much of the upcoming
workweek. For 24 hour rainfall totals, expect a widespread 4-6
inches of rain for this period for much of the upslope areas of the Olympics/Coastal Ranges/Cascades. The typical downslope areas in
due westerly flow, which includes metro Seattle and Portland,
should be spared the heaviest rainfall, with totals in the 1-2 inch
range in those metros likely to be more common. Soils in these
areas are already near saturation, which represents an average
amount of soil moisture going into today's big rainfall event, so
at least the second half of the rainfall should largely convert to
runoff, leading to significant rises in streams, creeks, and
eventually the rivers that drain the Willamette and Puget Sound
areas.=20

The abundance of Pacific moisture that will be moving into the
Pacific Northwest with the atmospheric river is originating from
the tropics well west of Hawaii. This plume of moisture is moving=20
over multiple thousands of miles of Pacific Ocean before it reaches
the coast, which is further enhancing the amount of moisture=20
available to fall as rain once that moisture plume runs into the
wall of mountains that is the coastal ranges and the Cascades.
Strong subtropical high pressure centered off the California coast
is directing the moisture plume's south side around its
northwestern periphery, while strong Pacific lows are drawing the
moisture northeastward on the plumes north side. This is acting to
focus locally enhance the rainfall within the moisture
plume/atmospheric river, which is why the heavy rain is
concentrated into western Washington and Oregon.

Expect that there will be a bit more "slop-over" of rainfall onto
the immediate downwind side of the Cascades and Olympics, so a few
minor expansions of the Marginal were made to include some of the
east-facing slopes of the Cascades, and a Slight Risk area
expansion was made on the east side of the Olympics.=20

...Northern Idaho and Adjacent Areas...

The inherited Marginal Risk was adjusted slightly to account for
small changes in the expected rainfall across interior areas of the
Pacific Northwest. The Marginal was trimmed from the Glacier N.P.
area due to most of the precipitation expected to fall as snow, but
expanded into far southeastern Washington and far northeastern
Oregon, where upslope potential will be increased in the terrain of
those areas. The A.R. will feature warm conditions, which will
raise snow levels to several thousand feet above ground level,
assuring that except in the highest elevations, the precipitation
type will be all rain, especially west of the Continental Divide.
While today should also bring the most rain to the area compared to
the upcoming several days, all of the soils in this area are nearly
saturated. In fact, recent colder weather and lower snow levels may
locally enhance the flash flooding threat once the heavier rain and
warmer temperatures move in as snowmelt becomes a contributing
factor to rising stream and river levels.=20

Wegman

Day 2
Valid 12Z Tue Dec 09 2025 - 12Z Wed Dec 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

...Western Washington and Oregon...

The atmospheric river (A.R.) plume on Tuesday morning will be=20
aimed at the northwestern quadrant of Oregon, after the plume=20
shifts south down the coast Monday night. The A.R. will remain
across northwestern Oregon for much of the day Tuesday. Expect an
additional 3-5 inches of rain across the west facing slopes of both
the coastal ranges and the Oregon and far southern Washington
Cascades during the day Tuesday. This will have followed the
roughly 3-5 inches of rain expected Monday night. Thus, expect high
creek, stream, and river levels by Tuesday night after all that
rainfall, as well as low-lying and urban flooding impacts. The
Slight Risk area remains largely unchanged.=20

By Tuesday night, a much weaker low than Monday's will track
northeast into British Columbia. This low will draw the A.R. back
towards the north before its trailing cold front plows into the
coast. This will reignite the heavy rainfall across much of western
Washington State, while rain rates trail off across west-central
Oregon. Unfortunately the heavy rain will continue into the coastal
ranges and far northern Oregon Cascades through the period. Expect
another 1-3 inches of rain along the Columbia River Tuesday night.
Rain rates will be notably lower than on Monday due to the weaker
low and a slightly weaker onshore flow at 850 (40-50 kts). Due to
the return of steady rain across the Olympics and central Cascades
Tuesday night, the inherited Slight Risk area was expanded north to
include portions of those ranges and their foothills. Meanwhile,
the highest peaks of the Cascades should still remain cold enough
for mostly snow.=20

...Northern Idaho and Adjacent Areas...

Weakening, but continuous 20-40 kt westerly flow at 850 across the
plains of eastern Washington will allow for locally heavy upslope
rain to continue into much of northern Idaho and northeastern
Oregon. The inherited Marginal is little changed, and mostly
reflects carving out the highest peaks expected to remain all or
mostly snow, while expanding into low lying areas where forecast
rainfall has increased. Regardless, snow levels will remain plenty
high enough to ensure all populated lower lying areas remain all
rain, and thus continue to pose a flooding threat.=20

Wegman

Day 3
Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

...Western Washington and Oregon...

The Slight Risk across portions of the Pacific Northwest remains
largely unchanged with this update. A northwest to southeast
oriented jet stream will remain in place from southern British
Columbia through to the northern Plains. This will put the Pacific
Northwest in the favorable right entrance region of the jet. A
series of upper level shortwaves will zip down the jet, which in
turn will keep the atmospheric river (A.R.) plume in place and
barely moving through the entire period. Due to the flow
orientation changing to out of the west-northwest. The moisture
will flow largely unimpeded through the Strait of Juan de Fuca and
past the coastal/Olympic ranges and into the Cascades. Thus, the
rainfall footprint is much more heavily skewed towards the Cascades
getting much heavier rainfall than the windward side of the coastal
ranges. That said, it will hardly be dry along the coast. Expect an
additional 3-5 inches of rain in the foothills of all of the
Washington Cascades through the period, while the coastal ranges
can expect just 1-3 inches of new rainfall. Given this setup, it
appears the most likely day where a future upgrade may be needed to
the ERO risk areas will be on Wednesday. This of course will be in
no small part due to the antecedent rainfall in nearly all areas
from both Monday and Tuesday, compounding high water concerns day
by day.=20

...Northern Idaho and Adjacent Areas...

A secondary peak of heavy precipitation into northern Idaho is
expected on Wednesday. The same A.R. impacting areas further west
will continue into the interior of the Pacific Northwest on
Wednesday as well. Renewed upslope flow into the west facing slopes
of the Rockies will re-enhance precipitation rates, as well as
raise snow levels after having crashed due to a brief cold air
intrusion on Tuesday. Thus, expect another round of snowmelt to go
along with the heavier rainfall rates. Just as further west, here
too the forecast will need to be monitored for a potential Slight
Risk upgrade with future updates. A large contributing factor to
the need for upgrades in both areas will be seeing what impacts
there are from the heavy rainfall expected especially today, but
possibly also again on Tuesday.

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5Hh95HCgjHgME5fYZqAQTC9cjVetXAub5kZzp6IkeDpq= MMjWQr6F0GjkNWb5Ju-Jww0OoMGc79ExgdCCKsYKxVpgomY$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5Hh95HCgjHgME5fYZqAQTC9cjVetXAub5kZzp6IkeDpq= MMjWQr6F0GjkNWb5Ju-Jww0OoMGc79ExgdCCKsYKvXxlJfk$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5Hh95HCgjHgME5fYZqAQTC9cjVetXAub5kZzp6IkeDpq= MMjWQr6F0GjkNWb5Ju-Jww0OoMGc79ExgdCCKsYKT9_4zVw$=20

=3D =3D =3D
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FOUS30 KWBC 081554
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1054 AM EST Mon Dec 8 2025

Day 1
Valid 12Z Mon Dec 08 2025 - 12Z Tue Dec 09 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

16z update:
Timing continues to be on track for strong surge of 1.25" total
PWat plume fairly perpendicular to the WA Coast with 50-60kts of
low to mid-level flow resulting in prolonged IVT values of 750 to
900 kg/m/s from about 18z-06z with very slow southward sag of
frontal zone toward the Columbia River by the end of the forecast
period. As to be expected, with initial loss of moisture crossing
the Coastal/Cascade ranges, moisture values decrease but remain
sufficient to support well above normal IVT values at or above 500
kg/m/s. There was some consideration for a small upgrade to a
Slight Risk across the Clearwater and northern Bitterroot Ranges,
but regionally higher FFG values suggest some better overall=20
retention of this first AR punch, as such, only small adjustments=20
were made for the downstream Marginal Risk currently in place.

12z CAM solutions continue the trend for mid to upper slopes of the Coastal/Cascade Ranges with widespread 4-6" with localized totals
of 8"+ by 09.12z; this while the main valleys should be less than=20
2". Soil conidtions are fairly saturated at 70-80% through 40cm,=20
especially within the foothills to suggest FFG values may be a bit=20 overestimated. Given the overlap, soil capacity will be reached=20
fairly quickly and much of the this initial surge of the AR will=20
result in solid runoff and elevated riverine rises. Please continue
to refer to local forecast office, Northwewst River Forecast=20
Center and National Water Center products and discussions for=20
expected river flooding conditions.

Gallina


...Western Washington and Oregon...

The inherited Slight Risk across Western Washington and Oregon
remains little changed this morning. A hauling 150+ kt upper level
jet will bring a vigorous shortwave trough into British Columbia
north of the Canadian border Monday afternoon and evening. The
trailing front associated with the surface low that is being
strengthened by that shortwave will plow into the coast Monday
afternoon. Behind that disturbance, mid-level 850 mb flow will
rapidly increase out of the due west at at least 50 kt, while PWATs
also rapidly increase from 0.75 inches to 1.25 inches as the head
of the incoming atmospheric river (A.R.) makes its way ashore. On
the synoptic scale, the overall rainfall footprint will be greatest
today as compared with the expected rainfall over the next few
days. This in turn will set the stage for multiple days of flooding
concerns as the rain continues through much of the upcoming
workweek. For 24 hour rainfall totals, expect a widespread 4-6
inches of rain for this period for much of the upslope areas of the Olympics/Coastal Ranges/Cascades. The typical downslope areas in
due westerly flow, which includes metro Seattle and Portland,
should be spared the heaviest rainfall, with totals in the 1-2 inch
range in those metros likely to be more common. Soils in these
areas are already near saturation, which represents an average
amount of soil moisture going into today's big rainfall event, so
at least the second half of the rainfall should largely convert to
runoff, leading to significant rises in streams, creeks, and
eventually the rivers that drain the Willamette and Puget Sound
areas.

The abundance of Pacific moisture that will be moving into the
Pacific Northwest with the atmospheric river is originating from
the tropics well west of Hawaii. This plume of moisture is moving
over multiple thousands of miles of Pacific Ocean before it reaches
the coast, which is further enhancing the amount of moisture
available to fall as rain once that moisture plume runs into the
wall of mountains that is the coastal ranges and the Cascades.
Strong subtropical high pressure centered off the California coast
is directing the moisture plume's south side around its
northwestern periphery, while strong Pacific lows are drawing the
moisture northeastward on the plumes north side. This is acting to
focus locally enhance the rainfall within the moisture
plume/atmospheric river, which is why the heavy rain is
concentrated into western Washington and Oregon.

Expect that there will be a bit more "slop-over" of rainfall onto
the immediate downwind side of the Cascades and Olympics, so a few
minor expansions of the Marginal were made to include some of the
east-facing slopes of the Cascades, and a Slight Risk area
expansion was made on the east side of the Olympics.

...Northern Idaho and Adjacent Areas...

The inherited Marginal Risk was adjusted slightly to account for
small changes in the expected rainfall across interior areas of the
Pacific Northwest. The Marginal was trimmed from the Glacier N.P.
area due to most of the precipitation expected to fall as snow, but
expanded into far southeastern Washington and far northeastern
Oregon, where upslope potential will be increased in the terrain of
those areas. The A.R. will feature warm conditions, which will
raise snow levels to several thousand feet above ground level,
assuring that except in the highest elevations, the precipitation
type will be all rain, especially west of the Continental Divide.
While today should also bring the most rain to the area compared to
the upcoming several days, all of the soils in this area are nearly
saturated. In fact, recent colder weather and lower snow levels may
locally enhance the flash flooding threat once the heavier rain and
warmer temperatures move in as snowmelt becomes a contributing
factor to rising stream and river levels.

Wegman

Day 2
Valid 12Z Tue Dec 09 2025 - 12Z Wed Dec 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

...Western Washington and Oregon...

The atmospheric river (A.R.) plume on Tuesday morning will be
aimed at the northwestern quadrant of Oregon, after the plume
shifts south down the coast Monday night. The A.R. will remain
across northwestern Oregon for much of the day Tuesday. Expect an
additional 3-5 inches of rain across the west facing slopes of both
the coastal ranges and the Oregon and far southern Washington
Cascades during the day Tuesday. This will have followed the
roughly 3-5 inches of rain expected Monday night. Thus, expect high
creek, stream, and river levels by Tuesday night after all that
rainfall, as well as low-lying and urban flooding impacts. The
Slight Risk area remains largely unchanged.

By Tuesday night, a much weaker low than Monday's will track
northeast into British Columbia. This low will draw the A.R. back
towards the north before its trailing cold front plows into the
coast. This will reignite the heavy rainfall across much of western
Washington State, while rain rates trail off across west-central
Oregon. Unfortunately the heavy rain will continue into the coastal
ranges and far northern Oregon Cascades through the period. Expect
another 1-3 inches of rain along the Columbia River Tuesday night.
Rain rates will be notably lower than on Monday due to the weaker
low and a slightly weaker onshore flow at 850 (40-50 kts). Due to
the return of steady rain across the Olympics and central Cascades
Tuesday night, the inherited Slight Risk area was expanded north to
include portions of those ranges and their foothills. Meanwhile,
the highest peaks of the Cascades should still remain cold enough
for mostly snow.

...Northern Idaho and Adjacent Areas...

Weakening, but continuous 20-40 kt westerly flow at 850 across the
plains of eastern Washington will allow for locally heavy upslope
rain to continue into much of northern Idaho and northeastern
Oregon. The inherited Marginal is little changed, and mostly
reflects carving out the highest peaks expected to remain all or
mostly snow, while expanding into low lying areas where forecast
rainfall has increased. Regardless, snow levels will remain plenty
high enough to ensure all populated lower lying areas remain all
rain, and thus continue to pose a flooding threat.

Wegman

Day 3
Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

...Western Washington and Oregon...

The Slight Risk across portions of the Pacific Northwest remains
largely unchanged with this update. A northwest to southeast
oriented jet stream will remain in place from southern British
Columbia through to the northern Plains. This will put the Pacific
Northwest in the favorable right entrance region of the jet. A
series of upper level shortwaves will zip down the jet, which in
turn will keep the atmospheric river (A.R.) plume in place and
barely moving through the entire period. Due to the flow
orientation changing to out of the west-northwest. The moisture
will flow largely unimpeded through the Strait of Juan de Fuca and
past the coastal/Olympic ranges and into the Cascades. Thus, the
rainfall footprint is much more heavily skewed towards the Cascades
getting much heavier rainfall than the windward side of the coastal
ranges. That said, it will hardly be dry along the coast. Expect an
additional 3-5 inches of rain in the foothills of all of the
Washington Cascades through the period, while the coastal ranges
can expect just 1-3 inches of new rainfall. Given this setup, it
appears the most likely day where a future upgrade may be needed to
the ERO risk areas will be on Wednesday. This of course will be in
no small part due to the antecedent rainfall in nearly all areas
from both Monday and Tuesday, compounding high water concerns day
by day.

...Northern Idaho and Adjacent Areas...

A secondary peak of heavy precipitation into northern Idaho is
expected on Wednesday. The same A.R. impacting areas further west
will continue into the interior of the Pacific Northwest on
Wednesday as well. Renewed upslope flow into the west facing slopes
of the Rockies will re-enhance precipitation rates, as well as
raise snow levels after having crashed due to a brief cold air
intrusion on Tuesday. Thus, expect another round of snowmelt to go
along with the heavier rainfall rates. Just as further west, here
too the forecast will need to be monitored for a potential Slight
Risk upgrade with future updates. A large contributing factor to
the need for upgrades in both areas will be seeing what impacts
there are from the heavy rainfall expected especially today, but
possibly also again on Tuesday.

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6DYjZKgWMFMM1ngH5J4isVAlLuNoKrbH7t634cUeuknG= GBzlZfQCPQIaH83iIy5DXh8Sqg1pjtoG0szX-9ckK6IBMlU$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6DYjZKgWMFMM1ngH5J4isVAlLuNoKrbH7t634cUeuknG= GBzlZfQCPQIaH83iIy5DXh8Sqg1pjtoG0szX-9ckrU8-YfQ$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6DYjZKgWMFMM1ngH5J4isVAlLuNoKrbH7t634cUeuknG= GBzlZfQCPQIaH83iIy5DXh8Sqg1pjtoG0szX-9ck4xMwrKs$=20

=3D =3D =3D
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FOUS30 KWBC 081949
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
249 PM EST Mon Dec 8 2025

Day 1
Valid 16Z Mon Dec 08 2025 - 12Z Tue Dec 09 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

16z update:
Timing continues to be on track for strong surge of 1.25" total
PWat plume fairly perpendicular to the WA Coast with 50-60kts of
low to mid-level flow resulting in prolonged IVT values of 750 to
900 kg/m/s from about 18z-06z with very slow southward sag of
frontal zone toward the Columbia River by the end of the forecast
period. As to be expected, with initial loss of moisture crossing
the Coastal/Cascade ranges, moisture values decrease but remain
sufficient to support well above normal IVT values at or above 500
kg/m/s. There was some consideration for a small upgrade to a
Slight Risk across the Clearwater and northern Bitterroot Ranges,
but regionally higher FFG values suggest some better overall
retention of this first AR punch, as such, only small adjustments
were made for the downstream Marginal Risk currently in place.

12z CAM solutions continue the trend for mid to upper slopes of the Coastal/Cascade Ranges with widespread 4-6" with localized totals
of 8"+ by 09.12z; this while the main valleys should be less than
2". Soil conditions are fairly saturated at 70-80% through 40cm,
especially within the foothills to suggest FFG values may be a bit overestimated. Given the overlap, soil capacity will be reached
fairly quickly and much of the this initial surge of the AR will
result in solid runoff and elevated riverine rises. Please continue
to refer to local forecast office, Northwest River Forecast Center
and National Water Center products and discussions for expected=20
river flooding conditions.

Gallina


...Western Washington and Oregon...

The inherited Slight Risk across Western Washington and Oregon
remains little changed this morning. A hauling 150+ kt upper level
jet will bring a vigorous shortwave trough into British Columbia
north of the Canadian border Monday afternoon and evening. The
trailing front associated with the surface low that is being
strengthened by that shortwave will plow into the coast Monday
afternoon. Behind that disturbance, mid-level 850 mb flow will
rapidly increase out of the due west at at least 50 kt, while PWATs
also rapidly increase from 0.75 inches to 1.25 inches as the head
of the incoming atmospheric river (A.R.) makes its way ashore. On
the synoptic scale, the overall rainfall footprint will be greatest
today as compared with the expected rainfall over the next few
days. This in turn will set the stage for multiple days of flooding
concerns as the rain continues through much of the upcoming
workweek. For 24 hour rainfall totals, expect a widespread 4-6
inches of rain for this period for much of the upslope areas of the Olympics/Coastal Ranges/Cascades. The typical downslope areas in
due westerly flow, which includes metro Seattle and Portland,
should be spared the heaviest rainfall, with totals in the 1-2 inch
range in those metros likely to be more common. Soils in these
areas are already near saturation, which represents an average
amount of soil moisture going into today's big rainfall event, so
at least the second half of the rainfall should largely convert to
runoff, leading to significant rises in streams, creeks, and
eventually the rivers that drain the Willamette and Puget Sound
areas.

The abundance of Pacific moisture that will be moving into the
Pacific Northwest with the atmospheric river is originating from
the tropics well west of Hawaii. This plume of moisture is moving
over multiple thousands of miles of Pacific Ocean before it reaches
the coast, which is further enhancing the amount of moisture
available to fall as rain once that moisture plume runs into the
wall of mountains that is the coastal ranges and the Cascades.
Strong subtropical high pressure centered off the California coast
is directing the moisture plume's south side around its
northwestern periphery, while strong Pacific lows are drawing the
moisture northeastward on the plumes north side. This is acting to
focus locally enhance the rainfall within the moisture
plume/atmospheric river, which is why the heavy rain is
concentrated into western Washington and Oregon.

Expect that there will be a bit more "slop-over" of rainfall onto
the immediate downwind side of the Cascades and Olympics, so a few
minor expansions of the Marginal were made to include some of the
east-facing slopes of the Cascades, and a Slight Risk area
expansion was made on the east side of the Olympics.

...Northern Idaho and Adjacent Areas...

The inherited Marginal Risk was adjusted slightly to account for
small changes in the expected rainfall across interior areas of the
Pacific Northwest. The Marginal was trimmed from the Glacier N.P.
area due to most of the precipitation expected to fall as snow, but
expanded into far southeastern Washington and far northeastern
Oregon, where upslope potential will be increased in the terrain of
those areas. The A.R. will feature warm conditions, which will
raise snow levels to several thousand feet above ground level,
assuring that except in the highest elevations, the precipitation
type will be all rain, especially west of the Continental Divide.
While today should also bring the most rain to the area compared to
the upcoming several days, all of the soils in this area are nearly
saturated. In fact, recent colder weather and lower snow levels may
locally enhance the flash flooding threat once the heavier rain and
warmer temperatures move in as snowmelt becomes a contributing
factor to rising stream and river levels.

Wegman

Day 2
Valid 12Z Tue Dec 09 2025 - 12Z Wed Dec 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

20z Update: Forecast generally looks on track and so only minimal=20
changes needed to the inherited risk areas. The IVT axis shifts=20
south and weakens Tuesday, but still enough onshore flow to support
a continued steady rainfall and flood risk across northwest OR.=20
The IVT axis shifts back north and intensifies between 00z-12z=20
Tuesday evening into Wednesday morning, likely resulting in an=20
increase in rainfall intensity from near the OR/WA border into=20
western WA. Given what should be saturated soil conditions by this=20
time, this additional rainfall will likely lead to another uptick=20
in flood impacts overnight into Wednesday morning.

Chenard

...Previous Discussion...

...Western Washington and Oregon...

The atmospheric river (A.R.) plume on Tuesday morning will be
aimed at the northwestern quadrant of Oregon, after the plume
shifts south down the coast Monday night. The A.R. will remain
across northwestern Oregon for much of the day Tuesday. Expect an
additional 3-5 inches of rain across the west facing slopes of both
the coastal ranges and the Oregon and far southern Washington
Cascades during the day Tuesday. This will have followed the
roughly 3-5 inches of rain expected Monday night. Thus, expect high
creek, stream, and river levels by Tuesday night after all that
rainfall, as well as low-lying and urban flooding impacts. The
Slight Risk area remains largely unchanged.

By Tuesday night, a much weaker low than Monday's will track
northeast into British Columbia. This low will draw the A.R. back
towards the north before its trailing cold front plows into the
coast. This will reignite the heavy rainfall across much of western
Washington State, while rain rates trail off across west-central
Oregon. Unfortunately the heavy rain will continue into the coastal
ranges and far northern Oregon Cascades through the period. Expect
another 1-3 inches of rain along the Columbia River Tuesday night.
Rain rates will be notably lower than on Monday due to the weaker
low and a slightly weaker onshore flow at 850 (40-50 kts). Due to
the return of steady rain across the Olympics and central Cascades
Tuesday night, the inherited Slight Risk area was expanded north to
include portions of those ranges and their foothills. Meanwhile,
the highest peaks of the Cascades should still remain cold enough
for mostly snow.

...Northern Idaho and Adjacent Areas...

Weakening, but continuous 20-40 kt westerly flow at 850 across the
plains of eastern Washington will allow for locally heavy upslope
rain to continue into much of northern Idaho and northeastern
Oregon. The inherited Marginal is little changed, and mostly
reflects carving out the highest peaks expected to remain all or
mostly snow, while expanding into low lying areas where forecast
rainfall has increased. Regardless, snow levels will remain plenty
high enough to ensure all populated lower lying areas remain all
rain, and thus continue to pose a flooding threat.

Wegman

Day 3
Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

20z Update: There has been a consistent northward trend in the=20
atmospheric river/moisture plume by Wednesday. Still looking at=20
additional heavy rainfall totals over western WA, but we were able=20
to trim back some of the southern extent of the risk area. Portions
of the WA Cascades are within the higher end of the Slight risk=20
probability range, as the increase in IVT over what should be=20
saturated ground conditions is likely to result in an increase in=20
the coverage and magnitude of flood impacts on Wednesday. There=20
remains some potential for an eventual MDT risk upgrade, however=20
the steady northward trend seen in the models does somewhat lower=20
confidence on exactly where the max rainfall axis will end up,
which precludes any upgrade at this time.

The higher terrain over northern ID and northwest MT still looks=20
on track to see 1 to 3 inches of rainfall, which combined with=20
snow melt, is likely to lead to at least some flooding impacts.=20
The aforementioned northward trend in the QPF axis applies here as
well, which introduces enough uncertainty to prevent a Slight risk
upgrade at the moment. Although if the current forecast holds=20
steady we very well could be looking at the need for a Slight risk=20
upgrade as the event nears.

Chenard


...Previous Discussion...

...Western Washington and Oregon...

The Slight Risk across portions of the Pacific Northwest remains
largely unchanged with this update. A northwest to southeast
oriented jet stream will remain in place from southern British
Columbia through to the northern Plains. This will put the Pacific
Northwest in the favorable right entrance region of the jet. A
series of upper level shortwaves will zip down the jet, which in
turn will keep the atmospheric river (A.R.) plume in place and
barely moving through the entire period. Due to the flow
orientation changing to out of the west-northwest. The moisture
will flow largely unimpeded through the Strait of Juan de Fuca and
past the coastal/Olympic ranges and into the Cascades. Thus, the
rainfall footprint is much more heavily skewed towards the Cascades
getting much heavier rainfall than the windward side of the coastal
ranges. That said, it will hardly be dry along the coast. Expect an
additional 3-5 inches of rain in the foothills of all of the
Washington Cascades through the period, while the coastal ranges
can expect just 1-3 inches of new rainfall. Given this setup, it
appears the most likely day where a future upgrade may be needed to
the ERO risk areas will be on Wednesday. This of course will be in
no small part due to the antecedent rainfall in nearly all areas
from both Monday and Tuesday, compounding high water concerns day
by day.

...Northern Idaho and Adjacent Areas...

A secondary peak of heavy precipitation into northern Idaho is
expected on Wednesday. The same A.R. impacting areas further west
will continue into the interior of the Pacific Northwest on
Wednesday as well. Renewed upslope flow into the west facing slopes
of the Rockies will re-enhance precipitation rates, as well as
raise snow levels after having crashed due to a brief cold air
intrusion on Tuesday. Thus, expect another round of snowmelt to go
along with the heavier rainfall rates. Just as further west, here
too the forecast will need to be monitored for a potential Slight
Risk upgrade with future updates. A large contributing factor to
the need for upgrades in both areas will be seeing what impacts
there are from the heavy rainfall expected especially today, but
possibly also again on Tuesday.

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9cn9izoVmR_ExDeE_prV3ysC6KQruNVtc_Cp6eFQbz9v= nsWaVf0q3Rej3W7jIe72WHChHmSU-GeBEZoO4iCXk5shzhY$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9cn9izoVmR_ExDeE_prV3ysC6KQruNVtc_Cp6eFQbz9v= nsWaVf0q3Rej3W7jIe72WHChHmSU-GeBEZoO4iCXm7fGSD8$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9cn9izoVmR_ExDeE_prV3ysC6KQruNVtc_Cp6eFQbz9v= nsWaVf0q3Rej3W7jIe72WHChHmSU-GeBEZoO4iCXy6I1K_Y$=20

=3D =3D =3D
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FOUS30 KWBC 090049
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
749 PM EST Mon Dec 8 2025

Day 1
Valid 01Z Tue Dec 09 2025 - 12Z Tue Dec 09 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

01Z Update...
Trends in radar and satellite imagery through late afternoon
suggest that the atmospheric river continues to evolve in a manner
close to the forecast...so overall few changes needed to the=20
09/01Z Excessive Rainfall Outlook and discussion. 00Z soundings=20
from Quillayute WA to Salem OR remain nearly saturated with=20
precipitable water values having increased to nearly 1.25 inches=20
since their soundings this morning...and the flow now being=20
perpendicular to the axis of the coastal ranges at 50+ kts. Still=20
expect the mid to upper slopes of the Coastal/Cascade Ranges to=20
received widespread amounts of 4-6 inches with localized totals of=20
8"+ by the end of the Day 1 period at 09/12Z. Please continue to=20
refer to local forecast office, Northwest River Forecast Center and
National Water Center products and discussions for expected river=20
flooding conditions.

Bann


16z update:
Timing continues to be on track for strong surge of 1.25" total
PWat plume fairly perpendicular to the WA Coast with 50-60kts of
low to mid-level flow resulting in prolonged IVT values of 750 to
900 kg/m/s from about 18z-06z with very slow southward sag of
frontal zone toward the Columbia River by the end of the forecast
period. As to be expected, with initial loss of moisture crossing
the Coastal/Cascade ranges, moisture values decrease but remain
sufficient to support well above normal IVT values at or above 500
kg/m/s. There was some consideration for a small upgrade to a
Slight Risk across the Clearwater and northern Bitterroot Ranges,
but regionally higher FFG values suggest some better overall
retention of this first AR punch, as such, only small adjustments
were made for the downstream Marginal Risk currently in place.

12z CAM solutions continue the trend for mid to upper slopes of the Coastal/Cascade Ranges with widespread 4-6" with localized totals
of 8"+ by 09.12z; this while the main valleys should be less than
2". Soil conditions are fairly saturated at 70-80% through 40cm,
especially within the foothills to suggest FFG values may be a bit overestimated. Given the overlap, soil capacity will be reached
fairly quickly and much of the this initial surge of the AR will
result in solid runoff and elevated riverine rises. Please continue
to refer to local forecast office, Northwest River Forecast Center
and National Water Center products and discussions for expected
river flooding conditions.

Gallina


...Western Washington and Oregon...

The inherited Slight Risk across Western Washington and Oregon
remains little changed this morning. A hauling 150+ kt upper level
jet will bring a vigorous shortwave trough into British Columbia
north of the Canadian border Monday afternoon and evening. The
trailing front associated with the surface low that is being
strengthened by that shortwave will plow into the coast Monday
afternoon. Behind that disturbance, mid-level 850 mb flow will
rapidly increase out of the due west at at least 50 kt, while PWATs
also rapidly increase from 0.75 inches to 1.25 inches as the head
of the incoming atmospheric river (A.R.) makes its way ashore. On
the synoptic scale, the overall rainfall footprint will be greatest
today as compared with the expected rainfall over the next few
days. This in turn will set the stage for multiple days of flooding
concerns as the rain continues through much of the upcoming
workweek. For 24 hour rainfall totals, expect a widespread 4-6
inches of rain for this period for much of the upslope areas of the Olympics/Coastal Ranges/Cascades. The typical downslope areas in
due westerly flow, which includes metro Seattle and Portland,
should be spared the heaviest rainfall, with totals in the 1-2 inch
range in those metros likely to be more common. Soils in these
areas are already near saturation, which represents an average
amount of soil moisture going into today's big rainfall event, so
at least the second half of the rainfall should largely convert to
runoff, leading to significant rises in streams, creeks, and
eventually the rivers that drain the Willamette and Puget Sound
areas.

The abundance of Pacific moisture that will be moving into the
Pacific Northwest with the atmospheric river is originating from
the tropics well west of Hawaii. This plume of moisture is moving
over multiple thousands of miles of Pacific Ocean before it reaches
the coast, which is further enhancing the amount of moisture
available to fall as rain once that moisture plume runs into the
wall of mountains that is the coastal ranges and the Cascades.
Strong subtropical high pressure centered off the California coast
is directing the moisture plume's south side around its
northwestern periphery, while strong Pacific lows are drawing the
moisture northeastward on the plumes north side. This is acting to
focus locally enhance the rainfall within the moisture
plume/atmospheric river, which is why the heavy rain is
concentrated into western Washington and Oregon.

Expect that there will be a bit more "slop-over" of rainfall onto
the immediate downwind side of the Cascades and Olympics, so a few
minor expansions of the Marginal were made to include some of the
east-facing slopes of the Cascades, and a Slight Risk area
expansion was made on the east side of the Olympics.

...Northern Idaho and Adjacent Areas...

The inherited Marginal Risk was adjusted slightly to account for
small changes in the expected rainfall across interior areas of the
Pacific Northwest. The Marginal was trimmed from the Glacier N.P.
area due to most of the precipitation expected to fall as snow, but
expanded into far southeastern Washington and far northeastern
Oregon, where upslope potential will be increased in the terrain of
those areas. The A.R. will feature warm conditions, which will
raise snow levels to several thousand feet above ground level,
assuring that except in the highest elevations, the precipitation
type will be all rain, especially west of the Continental Divide.
While today should also bring the most rain to the area compared to
the upcoming several days, all of the soils in this area are nearly
saturated. In fact, recent colder weather and lower snow levels may
locally enhance the flash flooding threat once the heavier rain and
warmer temperatures move in as snowmelt becomes a contributing
factor to rising stream and river levels.

Wegman

Day 2
Valid 12Z Tue Dec 09 2025 - 12Z Wed Dec 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

20z Update: Forecast generally looks on track and so only minimal
changes needed to the inherited risk areas. The IVT axis shifts
south and weakens Tuesday, but still enough onshore flow to support
a continued steady rainfall and flood risk across northwest OR.
The IVT axis shifts back north and intensifies between 00z-12z
Tuesday evening into Wednesday morning, likely resulting in an
increase in rainfall intensity from near the OR/WA border into
western WA. Given what should be saturated soil conditions by this
time, this additional rainfall will likely lead to another uptick
in flood impacts overnight into Wednesday morning.

Chenard

...Previous Discussion...

...Western Washington and Oregon...

The atmospheric river (A.R.) plume on Tuesday morning will be
aimed at the northwestern quadrant of Oregon, after the plume
shifts south down the coast Monday night. The A.R. will remain
across northwestern Oregon for much of the day Tuesday. Expect an
additional 3-5 inches of rain across the west facing slopes of both
the coastal ranges and the Oregon and far southern Washington
Cascades during the day Tuesday. This will have followed the
roughly 3-5 inches of rain expected Monday night. Thus, expect high
creek, stream, and river levels by Tuesday night after all that
rainfall, as well as low-lying and urban flooding impacts. The
Slight Risk area remains largely unchanged.

By Tuesday night, a much weaker low than Monday's will track
northeast into British Columbia. This low will draw the A.R. back
towards the north before its trailing cold front plows into the
coast. This will reignite the heavy rainfall across much of western
Washington State, while rain rates trail off across west-central
Oregon. Unfortunately the heavy rain will continue into the coastal
ranges and far northern Oregon Cascades through the period. Expect
another 1-3 inches of rain along the Columbia River Tuesday night.
Rain rates will be notably lower than on Monday due to the weaker
low and a slightly weaker onshore flow at 850 (40-50 kts). Due to
the return of steady rain across the Olympics and central Cascades
Tuesday night, the inherited Slight Risk area was expanded north to
include portions of those ranges and their foothills. Meanwhile,
the highest peaks of the Cascades should still remain cold enough
for mostly snow.

...Northern Idaho and Adjacent Areas...

Weakening, but continuous 20-40 kt westerly flow at 850 across the
plains of eastern Washington will allow for locally heavy upslope
rain to continue into much of northern Idaho and northeastern
Oregon. The inherited Marginal is little changed, and mostly
reflects carving out the highest peaks expected to remain all or
mostly snow, while expanding into low lying areas where forecast
rainfall has increased. Regardless, snow levels will remain plenty
high enough to ensure all populated lower lying areas remain all
rain, and thus continue to pose a flooding threat.

Wegman

Day 3
Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

20z Update: There has been a consistent northward trend in the
atmospheric river/moisture plume by Wednesday. Still looking at
additional heavy rainfall totals over western WA, but we were able
to trim back some of the southern extent of the risk area. Portions
of the WA Cascades are within the higher end of the Slight risk
probability range, as the increase in IVT over what should be
saturated ground conditions is likely to result in an increase in
the coverage and magnitude of flood impacts on Wednesday. There
remains some potential for an eventual MDT risk upgrade, however
the steady northward trend seen in the models does somewhat lower
confidence on exactly where the max rainfall axis will end up,
which precludes any upgrade at this time.

The higher terrain over northern ID and northwest MT still looks
on track to see 1 to 3 inches of rainfall, which combined with
snow melt, is likely to lead to at least some flooding impacts.
The aforementioned northward trend in the QPF axis applies here as
well, which introduces enough uncertainty to prevent a Slight risk
upgrade at the moment. Although if the current forecast holds
steady we very well could be looking at the need for a Slight risk
upgrade as the event nears.

Chenard


...Previous Discussion...

...Western Washington and Oregon...

The Slight Risk across portions of the Pacific Northwest remains
largely unchanged with this update. A northwest to southeast
oriented jet stream will remain in place from southern British
Columbia through to the northern Plains. This will put the Pacific
Northwest in the favorable right entrance region of the jet. A
series of upper level shortwaves will zip down the jet, which in
turn will keep the atmospheric river (A.R.) plume in place and
barely moving through the entire period. Due to the flow
orientation changing to out of the west-northwest. The moisture
will flow largely unimpeded through the Strait of Juan de Fuca and
past the coastal/Olympic ranges and into the Cascades. Thus, the
rainfall footprint is much more heavily skewed towards the Cascades
getting much heavier rainfall than the windward side of the coastal
ranges. That said, it will hardly be dry along the coast. Expect an
additional 3-5 inches of rain in the foothills of all of the
Washington Cascades through the period, while the coastal ranges
can expect just 1-3 inches of new rainfall. Given this setup, it
appears the most likely day where a future upgrade may be needed to
the ERO risk areas will be on Wednesday. This of course will be in
no small part due to the antecedent rainfall in nearly all areas
from both Monday and Tuesday, compounding high water concerns day
by day.

...Northern Idaho and Adjacent Areas...

A secondary peak of heavy precipitation into northern Idaho is
expected on Wednesday. The same A.R. impacting areas further west
will continue into the interior of the Pacific Northwest on
Wednesday as well. Renewed upslope flow into the west facing slopes
of the Rockies will re-enhance precipitation rates, as well as
raise snow levels after having crashed due to a brief cold air
intrusion on Tuesday. Thus, expect another round of snowmelt to go
along with the heavier rainfall rates. Just as further west, here
too the forecast will need to be monitored for a potential Slight
Risk upgrade with future updates. A large contributing factor to
the need for upgrades in both areas will be seeing what impacts
there are from the heavy rainfall expected especially today, but
possibly also again on Tuesday.

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9P3B_0iYkvOsgR2H0hYe5bjI72dVzx5pR10-pp-SA5Ov= nNb3WdjXto1wMJ7dZlJS58TP7z4IYI0919qtVKnc4C0vb4c$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9P3B_0iYkvOsgR2H0hYe5bjI72dVzx5pR10-pp-SA5Ov= nNb3WdjXto1wMJ7dZlJS58TP7z4IYI0919qtVKncLLP6VjE$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9P3B_0iYkvOsgR2H0hYe5bjI72dVzx5pR10-pp-SA5Ov= nNb3WdjXto1wMJ7dZlJS58TP7z4IYI0919qtVKncfgkMIi4$=20

=3D =3D =3D
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FOUS30 KWBC 090821
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
321 AM EST Tue Dec 9 2025

Day 1
Valid 12Z Tue Dec 09 2025 - 12Z Wed Dec 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

...Western Oregon and Washington...

The atmospheric river (A.R.) event is well underway across the
Pacific Northwest this morning. The plume of anomalous moisture
associated with the A.R. is currently aligned across northwestern
Oregon. Radar indicates rainfall rates are between 1/4 inch and 1/2
inch per hour. As is fairly typical of most A.R.s, the impact from
the rain isn't necessarily from the instantaneous rates from heavy
rain, but rather the long duration of steady rain, which can be
heavy at times on the windward (west-facing) sides of the coastal
ranges and the Cascades. A strong and vertically stacked
subtropical high is parked well off the California coast.
Meanwhile, frequent lows are tracking northeast across the
northeastern Pacific and slamming into the Canadian coast. The
trailing cold fronts are tapping into the plume of moisture that is
riding the gradient between the strong high to the south and the
lows to the north.

A Pacific low moved into the British Columbia coast earlier this
evening. This shoved the A.R. to its current position into
northwestern Oregon. As the next low tracks a little further north,
the subtropical high will begin ridging towards the north in
response. This will push the A.R. north with time. A moving A.R. is
usually a very good thing, as it reduces the time it's heavily
raining in any one area. Unfortunately this time, it will simply
move the A.R. back to the already hard hit areas of western
Washington that were hard hit yesterday. This northward shift is
expected this evening as the low moves ashore near Haida Gwaii, or
just south of the southern Alaska Panhandle. As the trailing front
follows into the Washington coast tonight, rainfall rates will=20
increase significantly as the A.R. aligns into Washington. This
will allow the rain rates to diminish substantially in most of
Oregon, though light rain near the Columbia River is likely to
continue to some much lesser degree. The A.R. is characterized by
PWATs to 1.25 inches, which is between 2 and 3 sigma above normal
for this time of year. Orthogonal westerly flow into the mountains
at 40-50 kt, which is plenty strong enough for substantial upslope enhancement.=20

In Oregon, expect the heavy rain, ongoing at present, to continue
for much of the day, while gradually shifting north and weakening.
In Washington the heaviest rain will be overnight tonight. The
Slight Risk area was expanded north with this update to include all
of the Olympic Peninsula as well as for a portion of the foothills
of the Cascades east of Seattle. The surrounding Marginal was
trimmed on the southern end in central Oregon as the trend
throughout the period will be a northward readjustment of the A.R.

...Northern Idaho and Adjacent Areas...

The Marginal Risk into northern Idaho, a small sliver of far
western Montana, and the northeast corner of Oregon is largely
unchanged with this update. Over the last 24 hours, the area has
seen anywhere from 1-1.5 inches of rain. At least that much is
expected over many of the same areas of the Sawtooths, Bitterroots,
and west into northeastern Oregon. Since the A.R. is originating
from the tropics, in addition to the anomalous moisture, much
warmer air will also accompany the rain, causing snow levels to
rise. Expect a significant snowmelt contribution to the rising
streams and rivers as a result. A Slight Risk upgrade may become
necessary if rainfall forecasts increase further through the day.
NASA Sport soil moisture analyses show that soils all across
northern Idaho are at saturation, so all new rainfall today will
convert to runoff. The impact of this runoff is unclear, hence the
possibility of a Slight Risk upgrade.

Wegman

Day 2
Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF WESTERN
WASHINGTON AS WELL AS FOR PORTIONS OF NORTHERN IDAHO AND FAR
WESTERN MONTANA...

...Western Washington...

The wettest day of the next 3 will be on Wednesday across much of
western Washington. The continuous westerly flow of 40-50 kt at 850
will continue off the Pacific through the day. A vigorous jet
streak to 150 kt will remain just north of Washington before diving southeastward across the upper high Plains. This will keep
Washington in the favorable right entrance region. A series of lows
will barrel into the British Columbia coast, each one keeping the
A.R. plume nearly stationary and highly energetic. Thus, widespread
4-6 inch rainfall totals are expected for the Olympics and the west
facing foothills of the Washington Cascades. As with most A.R.s,
very high snow levels will keep any snow confined to the highest
peaks of the far northern Cascades. This will keep the lion's share
of the expected precipitation as heavy rain for most of the
Cascades and certainly all of the coastal ranges as well. This
being the third day of more-or-less steady rainfall across much of
Washington, especially south of the Puget Sound area means the
soils are well past saturated, and all of the precipitation should
convert to runoff. Further, the high snow levels will promote
snowmelt as well, which will only further raise river levels.
Finally, the lows moving into the British Columbia coast will turn
the surface flow out of the WNW for a time, especially Wednesday
night. This will direct the flow straight down the strait of Juan
the Fuca and put the low-level flow just slightly off from
orthogonal to the mountains, favoring a slight northerly flow of
moisture down the foothills and the Puget Sound Region. This should
temper the downsloping side east of the mountains just a bit,
allowing for more rainfall into Seattle, Olympia, and the Puget
Sound region broadly. Thus, Wednesday and Wednesday night will also
be the wettest day in the urban cities as well.=20

Given all of the above, the inherited Slight Risk was expanded with
this update to include the Seattle metro and the surrounding areas
around southern Puget Sound with this update. A higher end Slight
was expanded south down the Cascades to near the Columbia
River/Oregon state line. Once the impacts from all the rainfall
seen across Western Washington become more clear, it will be easier
to ascertain what the impacts from this round of heavy rain on
Wednesday are likely to be. A Moderate Risk upgrade may be needed
with future updates or all or a portion of the Cascades and western
foothills with future updates.

...Northern Idaho and Far Western Montana...

The atmospheric river (A.R.) impacting Western Washington on
Wednesday will continue inland and impact the Rockies of northern
Idaho and western Montana as well on Wednesday. Just like further
west, the A.R. will cause snow levels to rise to as high as 8,000
ft. This will introduce a significant snowmelt component to the
resulting runoff from the upslope rainfall. Over the last 24 hours,
the area has picked up between 1-2 inches of rain, causing soils
to become fully saturated. Today, expect even more rain, with 2-3
inch totals expected to be common. The steady rain, snowmelt, and
abnormally warm conditions will increase the risk for avalanches in
the prone areas, especially where a heavy wet snow falls on top of
much weaker snow layers. Also expect an increase in rock and
landslides, as well as rising streams, creeks, rivers, and
localized urban flooding. Given all these expected impacts, a large
portion of northern Idaho and far western Montana were upgraded to
a Slight Risk with this update, and a smaller portion of northern
Idaho along the Montana state line from I-90 south is in a higher
end Slight Risk, as this area is expected to see the highest
rainfall amounts to around 3 inches through the period, almost all
of which falling as rain.

Wegman

Day 3
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
NORTHERN IDAHO...

...Northern Idaho and Western Montana...

A double upgrade from no risk area to a Slight Risk was introduced
for a portion of northern Idaho, generally south of I-90 and along
the Montana state line with this update. This upgrade was
introduced largely as a continuation of heavy rain from Wednesday
night across this region. Rainfall rates should be gradually
diminishing through the day Thursday, and as far as the heaviest
rain and immediate impacts, the rain on Wednesday should be more
impactful in this region. However, given the steady rain continues
into the day Thursday, the impacts resulting therefrom should also
continue. Meanwhile further east into Montana, a strong Arctic
front pushing south down the Plains should turn all of the
precipitation over central Montana over to snow. Thus, the flooding
threat is largely confined to northern Idaho and far western=20
Washington where the warm air associated with the A.R. will remain
in place on Thursday. Rock slides, avalanches, low-lying flooding,
sporadic urban impacts, and very high river levels will all be
ongoing Thursday morning over this area, supporting the Slight Risk
upgrade.

...Western Washington...

A Marginal Risk was expanded mainly for the Thursday morning time
period across much of western Washington with this update. This
expanded Marginal Risk includes the Seattle metro and the Puget
Sound area more broadly. As with further east, it will be a
continuation of the steady rain from Wednesday night into Thursday
across the area. It's likely a Slight Risk upgrade will be needed,
as the rain looks to take its time until Thursday afternoon to
significantly diminish in intensity. The A.R. event broadly will be
diminishing through this period. A large low well out over the
Pacific will take a more northward track, as compared to its
predecessors, as the pattern amplifies. This will effectively cut
off the A.R. as the moisture plume gets directed north towards the
Gulf of Alaska, and therefore, the flow with the A.R. shifts north
into British Columbia and substantially diminishes.=20

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8zxxDdhfNh8WxXry-EcDd_OY33vONbhUTbUNKQgw5cyX= a8z3DIHwcEoMYhE8YGHk7ymSON2sDotJ0fD3Y7Mt5izATIY$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8zxxDdhfNh8WxXry-EcDd_OY33vONbhUTbUNKQgw5cyX= a8z3DIHwcEoMYhE8YGHk7ymSON2sDotJ0fD3Y7MtJvdrdOQ$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8zxxDdhfNh8WxXry-EcDd_OY33vONbhUTbUNKQgw5cyX= a8z3DIHwcEoMYhE8YGHk7ymSON2sDotJ0fD3Y7Mtizw2jm4$=20

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FOUS30 KWBC 091550
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1050 AM EST Tue Dec 9 2025

Day 1
Valid 16Z Tue Dec 09 2025 - 12Z Wed Dec 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

16z Update: Forecast still looks on track so only minimal changes
needed to the inherited risk areas. Impacts should ramp up after=20
00z as the atmospheric river lifts back north and into western WA=20
and IVT magnitudes increase.

Chenard

...Previous Discussion...=20

...Western Oregon and Washington...

The atmospheric river (A.R.) event is well underway across the
Pacific Northwest this morning. The plume of anomalous moisture
associated with the A.R. is currently aligned across northwestern
Oregon. Radar indicates rainfall rates are between 1/4 inch and 1/2
inch per hour. As is fairly typical of most A.R.s, the impact from
the rain isn't necessarily from the instantaneous rates from heavy
rain, but rather the long duration of steady rain, which can be
heavy at times on the windward (west-facing) sides of the coastal
ranges and the Cascades. A strong and vertically stacked
subtropical high is parked well off the California coast.
Meanwhile, frequent lows are tracking northeast across the
northeastern Pacific and slamming into the Canadian coast. The
trailing cold fronts are tapping into the plume of moisture that is
riding the gradient between the strong high to the south and the
lows to the north.

A Pacific low moved into the British Columbia coast earlier this
evening. This shoved the A.R. to its current position into
northwestern Oregon. As the next low tracks a little further north,
the subtropical high will begin ridging towards the north in
response. This will push the A.R. north with time. A moving A.R. is
usually a very good thing, as it reduces the time it's heavily
raining in any one area. Unfortunately this time, it will simply
move the A.R. back to the already hard hit areas of western
Washington that were hard hit yesterday. This northward shift is
expected this evening as the low moves ashore near Haida Gwaii, or
just south of the southern Alaska Panhandle. As the trailing front
follows into the Washington coast tonight, rainfall rates will
increase significantly as the A.R. aligns into Washington. This
will allow the rain rates to diminish substantially in most of
Oregon, though light rain near the Columbia River is likely to
continue to some much lesser degree. The A.R. is characterized by
PWATs to 1.25 inches, which is between 2 and 3 sigma above normal
for this time of year. Orthogonal westerly flow into the mountains
at 40-50 kt, which is plenty strong enough for substantial upslope
enhancement.

In Oregon, expect the heavy rain, ongoing at present, to continue
for much of the day, while gradually shifting north and weakening.
In Washington the heaviest rain will be overnight tonight. The
Slight Risk area was expanded north with this update to include all
of the Olympic Peninsula as well as for a portion of the foothills
of the Cascades east of Seattle. The surrounding Marginal was
trimmed on the southern end in central Oregon as the trend
throughout the period will be a northward readjustment of the A.R.

...Northern Idaho and Adjacent Areas...

The Marginal Risk into northern Idaho, a small sliver of far
western Montana, and the northeast corner of Oregon is largely
unchanged with this update. Over the last 24 hours, the area has
seen anywhere from 1-1.5 inches of rain. At least that much is
expected over many of the same areas of the Sawtooths, Bitterroots,
and west into northeastern Oregon. Since the A.R. is originating
from the tropics, in addition to the anomalous moisture, much
warmer air will also accompany the rain, causing snow levels to
rise. Expect a significant snowmelt contribution to the rising
streams and rivers as a result. A Slight Risk upgrade may become
necessary if rainfall forecasts increase further through the day.
NASA Sport soil moisture analyses show that soils all across
northern Idaho are at saturation, so all new rainfall today will
convert to runoff. The impact of this runoff is unclear, hence the
possibility of a Slight Risk upgrade.

Wegman

Day 2
Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF WESTERN
WASHINGTON AS WELL AS FOR PORTIONS OF NORTHERN IDAHO AND FAR
WESTERN MONTANA...

...Western Washington...

The wettest day of the next 3 will be on Wednesday across much of
western Washington. The continuous westerly flow of 40-50 kt at 850
will continue off the Pacific through the day. A vigorous jet
streak to 150 kt will remain just north of Washington before diving southeastward across the upper high Plains. This will keep
Washington in the favorable right entrance region. A series of lows
will barrel into the British Columbia coast, each one keeping the
A.R. plume nearly stationary and highly energetic. Thus, widespread
4-6 inch rainfall totals are expected for the Olympics and the west
facing foothills of the Washington Cascades. As with most A.R.s,
very high snow levels will keep any snow confined to the highest
peaks of the far northern Cascades. This will keep the lion's share
of the expected precipitation as heavy rain for most of the
Cascades and certainly all of the coastal ranges as well. This
being the third day of more-or-less steady rainfall across much of
Washington, especially south of the Puget Sound area means the
soils are well past saturated, and all of the precipitation should
convert to runoff. Further, the high snow levels will promote
snowmelt as well, which will only further raise river levels.
Finally, the lows moving into the British Columbia coast will turn
the surface flow out of the WNW for a time, especially Wednesday
night. This will direct the flow straight down the strait of Juan
the Fuca and put the low-level flow just slightly off from
orthogonal to the mountains, favoring a slight northerly flow of
moisture down the foothills and the Puget Sound Region. This should
temper the downsloping side east of the mountains just a bit,
allowing for more rainfall into Seattle, Olympia, and the Puget
Sound region broadly. Thus, Wednesday and Wednesday night will also
be the wettest day in the urban cities as well.

Given all of the above, the inherited Slight Risk was expanded with
this update to include the Seattle metro and the surrounding areas
around southern Puget Sound with this update. A higher end Slight
was expanded south down the Cascades to near the Columbia
River/Oregon state line. Once the impacts from all the rainfall
seen across Western Washington become more clear, it will be easier
to ascertain what the impacts from this round of heavy rain on
Wednesday are likely to be. A Moderate Risk upgrade may be needed
with future updates or all or a portion of the Cascades and western
foothills with future updates.

...Northern Idaho and Far Western Montana...

The atmospheric river (A.R.) impacting Western Washington on
Wednesday will continue inland and impact the Rockies of northern
Idaho and western Montana as well on Wednesday. Just like further
west, the A.R. will cause snow levels to rise to as high as 8,000
ft. This will introduce a significant snowmelt component to the
resulting runoff from the upslope rainfall. Over the last 24 hours,
the area has picked up between 1-2 inches of rain, causing soils
to become fully saturated. Today, expect even more rain, with 2-3
inch totals expected to be common. The steady rain, snowmelt, and
abnormally warm conditions will increase the risk for avalanches in
the prone areas, especially where a heavy wet snow falls on top of
much weaker snow layers. Also expect an increase in rock and
landslides, as well as rising streams, creeks, rivers, and
localized urban flooding. Given all these expected impacts, a large
portion of northern Idaho and far western Montana were upgraded to
a Slight Risk with this update, and a smaller portion of northern
Idaho along the Montana state line from I-90 south is in a higher
end Slight Risk, as this area is expected to see the highest
rainfall amounts to around 3 inches through the period, almost all
of which falling as rain.

Wegman

Day 3
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
NORTHERN IDAHO...

...Northern Idaho and Western Montana...

A double upgrade from no risk area to a Slight Risk was introduced
for a portion of northern Idaho, generally south of I-90 and along
the Montana state line with this update. This upgrade was
introduced largely as a continuation of heavy rain from Wednesday
night across this region. Rainfall rates should be gradually
diminishing through the day Thursday, and as far as the heaviest
rain and immediate impacts, the rain on Wednesday should be more
impactful in this region. However, given the steady rain continues
into the day Thursday, the impacts resulting therefrom should also
continue. Meanwhile further east into Montana, a strong Arctic
front pushing south down the Plains should turn all of the
precipitation over central Montana over to snow. Thus, the flooding
threat is largely confined to northern Idaho and far western
Washington where the warm air associated with the A.R. will remain
in place on Thursday. Rock slides, avalanches, low-lying flooding,
sporadic urban impacts, and very high river levels will all be
ongoing Thursday morning over this area, supporting the Slight Risk
upgrade.

...Western Washington...

A Marginal Risk was expanded mainly for the Thursday morning time
period across much of western Washington with this update. This
expanded Marginal Risk includes the Seattle metro and the Puget
Sound area more broadly. As with further east, it will be a
continuation of the steady rain from Wednesday night into Thursday
across the area. It's likely a Slight Risk upgrade will be needed,
as the rain looks to take its time until Thursday afternoon to
significantly diminish in intensity. The A.R. event broadly will be
diminishing through this period. A large low well out over the
Pacific will take a more northward track, as compared to its
predecessors, as the pattern amplifies. This will effectively cut
off the A.R. as the moisture plume gets directed north towards the
Gulf of Alaska, and therefore, the flow with the A.R. shifts north
into British Columbia and substantially diminishes.

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_Vu226vQNWjBQ27w1LIgtkJbBI16kqPVgA8hzKAR8axw= uoLgN9A7Uoa0Y78bZYnB1cOb2anC_N4l_a2yiWoB6A076YY$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_Vu226vQNWjBQ27w1LIgtkJbBI16kqPVgA8hzKAR8axw= uoLgN9A7Uoa0Y78bZYnB1cOb2anC_N4l_a2yiWoBS2VV8MU$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_Vu226vQNWjBQ27w1LIgtkJbBI16kqPVgA8hzKAR8axw= uoLgN9A7Uoa0Y78bZYnB1cOb2anC_N4l_a2yiWoBv26NIms$=20

=3D =3D =3D
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FOUS30 KWBC 092049
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
349 PM EST Tue Dec 9 2025

Day 1
Valid 16Z Tue Dec 09 2025 - 12Z Wed Dec 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

16z Update: Forecast still looks on track so only minimal changes
needed to the inherited risk areas. Impacts should ramp up after
00z as the atmospheric river lifts back north and into western WA
and IVT magnitudes increase.

Chenard

...Previous Discussion...

...Western Oregon and Washington...

The atmospheric river (A.R.) event is well underway across the
Pacific Northwest this morning. The plume of anomalous moisture
associated with the A.R. is currently aligned across northwestern
Oregon. Radar indicates rainfall rates are between 1/4 inch and 1/2
inch per hour. As is fairly typical of most A.R.s, the impact from
the rain isn't necessarily from the instantaneous rates from heavy
rain, but rather the long duration of steady rain, which can be
heavy at times on the windward (west-facing) sides of the coastal
ranges and the Cascades. A strong and vertically stacked
subtropical high is parked well off the California coast.
Meanwhile, frequent lows are tracking northeast across the
northeastern Pacific and slamming into the Canadian coast. The
trailing cold fronts are tapping into the plume of moisture that is
riding the gradient between the strong high to the south and the
lows to the north.

A Pacific low moved into the British Columbia coast earlier this
evening. This shoved the A.R. to its current position into
northwestern Oregon. As the next low tracks a little further north,
the subtropical high will begin ridging towards the north in
response. This will push the A.R. north with time. A moving A.R. is
usually a very good thing, as it reduces the time it's heavily
raining in any one area. Unfortunately this time, it will simply
move the A.R. back to the already hard hit areas of western
Washington that were hard hit yesterday. This northward shift is
expected this evening as the low moves ashore near Haida Gwaii, or
just south of the southern Alaska Panhandle. As the trailing front
follows into the Washington coast tonight, rainfall rates will
increase significantly as the A.R. aligns into Washington. This
will allow the rain rates to diminish substantially in most of
Oregon, though light rain near the Columbia River is likely to
continue to some much lesser degree. The A.R. is characterized by
PWATs to 1.25 inches, which is between 2 and 3 sigma above normal
for this time of year. Orthogonal westerly flow into the mountains
at 40-50 kt, which is plenty strong enough for substantial upslope
enhancement.

In Oregon, expect the heavy rain, ongoing at present, to continue
for much of the day, while gradually shifting north and weakening.
In Washington the heaviest rain will be overnight tonight. The
Slight Risk area was expanded north with this update to include all
of the Olympic Peninsula as well as for a portion of the foothills
of the Cascades east of Seattle. The surrounding Marginal was
trimmed on the southern end in central Oregon as the trend
throughout the period will be a northward readjustment of the A.R.

...Northern Idaho and Adjacent Areas...

The Marginal Risk into northern Idaho, a small sliver of far
western Montana, and the northeast corner of Oregon is largely
unchanged with this update. Over the last 24 hours, the area has
seen anywhere from 1-1.5 inches of rain. At least that much is
expected over many of the same areas of the Sawtooths, Bitterroots,
and west into northeastern Oregon. Since the A.R. is originating
from the tropics, in addition to the anomalous moisture, much
warmer air will also accompany the rain, causing snow levels to
rise. Expect a significant snowmelt contribution to the rising
streams and rivers as a result. A Slight Risk upgrade may become
necessary if rainfall forecasts increase further through the day.
NASA Sport soil moisture analyses show that soils all across
northern Idaho are at saturation, so all new rainfall today will
convert to runoff. The impact of this runoff is unclear, hence the
possibility of a Slight Risk upgrade.

Wegman

Day 2
Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF WESTERN
WASHINGTON AS WELL AS FOR PORTIONS OF NORTHERN IDAHO AND FAR
WESTERN MONTANA...

2100 UTC update: No significant changes made to the previous
outlook areas across the coastal Pac NW and Northern Rockies. Edits
to the previous areas were mostly to better fit latest qpf and
snowfall forecasts.

Oravec

...Previous discussion...

...Western Washington...

The wettest day of the next 3 will be on Wednesday across much of
western Washington. The continuous westerly flow of 40-50 kt at 850
will continue off the Pacific through the day. A vigorous jet
streak to 150 kt will remain just north of Washington before diving southeastward across the upper high Plains. This will keep
Washington in the favorable right entrance region. A series of lows
will barrel into the British Columbia coast, each one keeping the
A.R. plume nearly stationary and highly energetic. Thus, widespread
4-6 inch rainfall totals are expected for the Olympics and the west
facing foothills of the Washington Cascades. As with most A.R.s,
very high snow levels will keep any snow confined to the highest
peaks of the far northern Cascades. This will keep the lion's share
of the expected precipitation as heavy rain for most of the
Cascades and certainly all of the coastal ranges as well. This
being the third day of more-or-less steady rainfall across much of
Washington, especially south of the Puget Sound area means the
soils are well past saturated, and all of the precipitation should
convert to runoff. Further, the high snow levels will promote
snowmelt as well, which will only further raise river levels.
Finally, the lows moving into the British Columbia coast will turn
the surface flow out of the WNW for a time, especially Wednesday
night. This will direct the flow straight down the strait of Juan
the Fuca and put the low-level flow just slightly off from
orthogonal to the mountains, favoring a slight northerly flow of
moisture down the foothills and the Puget Sound Region. This should
temper the downsloping side east of the mountains just a bit,
allowing for more rainfall into Seattle, Olympia, and the Puget
Sound region broadly. Thus, Wednesday and Wednesday night will also
be the wettest day in the urban cities as well.

Given all of the above, the inherited Slight Risk was expanded with
this update to include the Seattle metro and the surrounding areas
around southern Puget Sound with this update. A higher end Slight
was expanded south down the Cascades to near the Columbia
River/Oregon state line. Once the impacts from all the rainfall
seen across Western Washington become more clear, it will be easier
to ascertain what the impacts from this round of heavy rain on
Wednesday are likely to be. A Moderate Risk upgrade may be needed
with future updates or all or a portion of the Cascades and western
foothills with future updates.

...Northern Idaho and Far Western Montana...

The atmospheric river (A.R.) impacting Western Washington on
Wednesday will continue inland and impact the Rockies of northern
Idaho and western Montana as well on Wednesday. Just like further
west, the A.R. will cause snow levels to rise to as high as 8,000
ft. This will introduce a significant snowmelt component to the
resulting runoff from the upslope rainfall. Over the last 24 hours,
the area has picked up between 1-2 inches of rain, causing soils
to become fully saturated. Today, expect even more rain, with 2-3
inch totals expected to be common. The steady rain, snowmelt, and
abnormally warm conditions will increase the risk for avalanches in
the prone areas, especially where a heavy wet snow falls on top of
much weaker snow layers. Also expect an increase in rock and
landslides, as well as rising streams, creeks, rivers, and
localized urban flooding. Given all these expected impacts, a large
portion of northern Idaho and far western Montana were upgraded to
a Slight Risk with this update, and a smaller portion of northern
Idaho along the Montana state line from I-90 south is in a higher
end Slight Risk, as this area is expected to see the highest
rainfall amounts to around 3 inches through the period, almost all
of which falling as rain.

Wegman

Day 3
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
NORTHERN IDAHO...

2100 UTC update: The previous slight risk area over northern ID was
decreased in size to better fit the latest day 3 qpf. The previous
marginal risk area was removed along the WA coast, into far
northern OR coast based on the latest light day 3 qpf across these
areas. The marginal risk was confined to the upslope area of the WA
Cascades.

Oravec

...Previous discussion...


...Northern Idaho and Western Montana...

A double upgrade from no risk area to a Slight Risk was introduced
for a portion of northern Idaho, generally south of I-90 and along
the Montana state line with this update. This upgrade was
introduced largely as a continuation of heavy rain from Wednesday
night across this region. Rainfall rates should be gradually
diminishing through the day Thursday, and as far as the heaviest
rain and immediate impacts, the rain on Wednesday should be more
impactful in this region. However, given the steady rain continues
into the day Thursday, the impacts resulting therefrom should also
continue. Meanwhile further east into Montana, a strong Arctic
front pushing south down the Plains should turn all of the
precipitation over central Montana over to snow. Thus, the flooding
threat is largely confined to northern Idaho and far western
Washington where the warm air associated with the A.R. will remain
in place on Thursday. Rock slides, avalanches, low-lying flooding,
sporadic urban impacts, and very high river levels will all be
ongoing Thursday morning over this area, supporting the Slight Risk
upgrade.

...Western Washington...

A Marginal Risk was expanded mainly for the Thursday morning time
period across much of western Washington with this update. This
expanded Marginal Risk includes the Seattle metro and the Puget
Sound area more broadly. As with further east, it will be a
continuation of the steady rain from Wednesday night into Thursday
across the area. It's likely a Slight Risk upgrade will be needed,
as the rain looks to take its time until Thursday afternoon to
significantly diminish in intensity. The A.R. event broadly will be
diminishing through this period. A large low well out over the
Pacific will take a more northward track, as compared to its
predecessors, as the pattern amplifies. This will effectively cut
off the A.R. as the moisture plume gets directed north towards the
Gulf of Alaska, and therefore, the flow with the A.R. shifts north
into British Columbia and substantially diminishes.

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!63FMrM0JprAiXRsWERzYy8WHPsya2-WC-r_kMQemiTy8= BjaIaXw3rV4FATCwXBf86iRp544ZTlSAGjSieCFLwMACCZg$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!63FMrM0JprAiXRsWERzYy8WHPsya2-WC-r_kMQemiTy8= BjaIaXw3rV4FATCwXBf86iRp544ZTlSAGjSieCFLvgXpuJ4$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!63FMrM0JprAiXRsWERzYy8WHPsya2-WC-r_kMQemiTy8= BjaIaXw3rV4FATCwXBf86iRp544ZTlSAGjSieCFLD1It6No$=20

=3D =3D =3D
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FOUS30 KWBC 100056
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
756 PM EST Tue Dec 9 2025

Day 1
Valid 01Z Wed Dec 10 2025 - 12Z Wed Dec 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

...Western Oregon and Washington...

The atmospheric river event will continue across the Pacific=20
Northwest tonight as the next surge of heavy rain reaches=20
Washington. As of 00Z, steady light to moderate with occasional=20
heavy rain was ongoing across northern Oregon, but rates have=20
tapered off compared to earlier Tuesday morning. Ahead of an=20
approaching cold front, a plume of IVT with magnitudes in the=20
500-750 kg/m/s range along the northern Oregon coast will translate
north and increase in magnitude into the 800-1000 kg/m/s range=20
along coastal Washington into the southern portions of the Puget=20
Sound through Wednesday morning.

The probability of hourly rainfall in excess of 0.5 inches will=20
increase overnight, especially into the 06-12Z time frame across=20
the Olympics into the northern Cascades. 850-700 mb mean layer=20
winds of 50 to 60+ kt are expected across western Washington,=20
coupled with precipitable water values of roughly 1.2 to 1.4=20
inches. Snow levels will also increase with the surge of warmer air
lifting north, with all rain below elevations of 9,000 to 10,000=20
feet.=20

Peak 12 hour rainfall totals through 12Z Wednesday are forecast to
range between 2-4 inches from the Olympics into the northern=20
Cascades. The forecast rain rates and additional rainfall through=20
12Z carry an increased flood threat on area rivers/streams due to=20
roughly 5 to 10 inches of rain which have fallen over the past 3=20
days, most over the past 24-36 hours. In addition to potential=20
flooding of low-lying and urban locations, the potential will also=20
exist for landslides and debris flows due to the increase in=20
rainfall intensity overnight.

...Northern Idaho and Adjacent Areas...

The Marginal Risk across northern Idaho into neighboring western=20
Montana, northeastern Oregon and southeastern Washington remains=20
unchanged with this update. Similar to coastal locations of the=20
Pacific Northwest, heavier rainfall intensities are expected in the
06-12Z time frame tonight. Hourly rainfall potential will increase
up to and beyond 12Z Wednesday with peak values generally under=20
0.3 inches, but the Blue Mountains of northeastern Oregon will have
potential for peak hourly rainfall of 0.3 to 0.4+ inches=20
overnight. Total peak 12 hour rainfall of 1 to 1.5 inches is=20
expected (close to 2 inches for the Blues) through 12Z with=20
snowmelt contributing to rising streams and rivers. Given increased
soil moisture due to antecedent rainfall, localized impacts of=20
heavy rain will remain possible.

Otto


Day 2
Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF WESTERN
WASHINGTON AS WELL AS FOR PORTIONS OF NORTHERN IDAHO AND FAR
WESTERN MONTANA...

2100 UTC update: No significant changes made to the previous
outlook areas across the coastal Pac NW and Northern Rockies. Edits
to the previous areas were mostly to better fit latest qpf and
snowfall forecasts.

Oravec

...Previous discussion...

...Western Washington...

The wettest day of the next 3 will be on Wednesday across much of
western Washington. The continuous westerly flow of 40-50 kt at 850
will continue off the Pacific through the day. A vigorous jet
streak to 150 kt will remain just north of Washington before diving southeastward across the upper high Plains. This will keep
Washington in the favorable right entrance region. A series of lows
will barrel into the British Columbia coast, each one keeping the
A.R. plume nearly stationary and highly energetic. Thus, widespread
4-6 inch rainfall totals are expected for the Olympics and the west
facing foothills of the Washington Cascades. As with most A.R.s,
very high snow levels will keep any snow confined to the highest
peaks of the far northern Cascades. This will keep the lion's share
of the expected precipitation as heavy rain for most of the
Cascades and certainly all of the coastal ranges as well. This
being the third day of more-or-less steady rainfall across much of
Washington, especially south of the Puget Sound area means the
soils are well past saturated, and all of the precipitation should
convert to runoff. Further, the high snow levels will promote
snowmelt as well, which will only further raise river levels.
Finally, the lows moving into the British Columbia coast will turn
the surface flow out of the WNW for a time, especially Wednesday
night. This will direct the flow straight down the strait of Juan
the Fuca and put the low-level flow just slightly off from
orthogonal to the mountains, favoring a slight northerly flow of
moisture down the foothills and the Puget Sound Region. This should
temper the downsloping side east of the mountains just a bit,
allowing for more rainfall into Seattle, Olympia, and the Puget
Sound region broadly. Thus, Wednesday and Wednesday night will also
be the wettest day in the urban cities as well.

Given all of the above, the inherited Slight Risk was expanded with
this update to include the Seattle metro and the surrounding areas
around southern Puget Sound with this update. A higher end Slight
was expanded south down the Cascades to near the Columbia
River/Oregon state line. Once the impacts from all the rainfall
seen across Western Washington become more clear, it will be easier
to ascertain what the impacts from this round of heavy rain on
Wednesday are likely to be. A Moderate Risk upgrade may be needed
with future updates or all or a portion of the Cascades and western
foothills with future updates.

...Northern Idaho and Far Western Montana...

The atmospheric river (A.R.) impacting Western Washington on
Wednesday will continue inland and impact the Rockies of northern
Idaho and western Montana as well on Wednesday. Just like further
west, the A.R. will cause snow levels to rise to as high as 8,000
ft. This will introduce a significant snowmelt component to the
resulting runoff from the upslope rainfall. Over the last 24 hours,
the area has picked up between 1-2 inches of rain, causing soils
to become fully saturated. Today, expect even more rain, with 2-3
inch totals expected to be common. The steady rain, snowmelt, and
abnormally warm conditions will increase the risk for avalanches in
the prone areas, especially where a heavy wet snow falls on top of
much weaker snow layers. Also expect an increase in rock and
landslides, as well as rising streams, creeks, rivers, and
localized urban flooding. Given all these expected impacts, a large
portion of northern Idaho and far western Montana were upgraded to
a Slight Risk with this update, and a smaller portion of northern
Idaho along the Montana state line from I-90 south is in a higher
end Slight Risk, as this area is expected to see the highest
rainfall amounts to around 3 inches through the period, almost all
of which falling as rain.

Wegman

Day 3
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
NORTHERN IDAHO...

2100 UTC update: The previous slight risk area over northern ID was
decreased in size to better fit the latest day 3 qpf. The previous
marginal risk area was removed along the WA coast, into far
northern OR coast based on the latest light day 3 qpf across these
areas. The marginal risk was confined to the upslope area of the WA
Cascades.

Oravec

...Previous discussion...


...Northern Idaho and Western Montana...

A double upgrade from no risk area to a Slight Risk was introduced
for a portion of northern Idaho, generally south of I-90 and along
the Montana state line with this update. This upgrade was
introduced largely as a continuation of heavy rain from Wednesday
night across this region. Rainfall rates should be gradually
diminishing through the day Thursday, and as far as the heaviest
rain and immediate impacts, the rain on Wednesday should be more
impactful in this region. However, given the steady rain continues
into the day Thursday, the impacts resulting therefrom should also
continue. Meanwhile further east into Montana, a strong Arctic
front pushing south down the Plains should turn all of the
precipitation over central Montana over to snow. Thus, the flooding
threat is largely confined to northern Idaho and far western
Washington where the warm air associated with the A.R. will remain
in place on Thursday. Rock slides, avalanches, low-lying flooding,
sporadic urban impacts, and very high river levels will all be
ongoing Thursday morning over this area, supporting the Slight Risk
upgrade.

...Western Washington...

A Marginal Risk was expanded mainly for the Thursday morning time
period across much of western Washington with this update. This
expanded Marginal Risk includes the Seattle metro and the Puget
Sound area more broadly. As with further east, it will be a
continuation of the steady rain from Wednesday night into Thursday
across the area. It's likely a Slight Risk upgrade will be needed,
as the rain looks to take its time until Thursday afternoon to
significantly diminish in intensity. The A.R. event broadly will be
diminishing through this period. A large low well out over the
Pacific will take a more northward track, as compared to its
predecessors, as the pattern amplifies. This will effectively cut
off the A.R. as the moisture plume gets directed north towards the
Gulf of Alaska, and therefore, the flow with the A.R. shifts north
into British Columbia and substantially diminishes.

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-Wbn7Te9c7pbBzrByKOqJyHAYVemc2ymNmLY572lvAKF= MTDZJ6pXQLP8DN4lfA7vfdOMDNtTDBNHvmYsp7tJQzZABko$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-Wbn7Te9c7pbBzrByKOqJyHAYVemc2ymNmLY572lvAKF= MTDZJ6pXQLP8DN4lfA7vfdOMDNtTDBNHvmYsp7tJQfSA_w4$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-Wbn7Te9c7pbBzrByKOqJyHAYVemc2ymNmLY572lvAKF= MTDZJ6pXQLP8DN4lfA7vfdOMDNtTDBNHvmYsp7tJalJUwbk$=20

=3D =3D =3D
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FOUS30 KWBC 100830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
330 AM EST Wed Dec 10 2025

Day 1
Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF WESTERN
WASHINGTON AS WELL AS FOR PORTIONS OF NORTHERN IDAHO AND FAR
WESTERN MONTANA...

...Western Washington...

An atmospheric river is currently impacting much of Washington
State this morning. The narrow but intense plume of deep tropical
moisture originating from near Hawaii is being drawn northeastward
by a strong subtropical high that is parked off the California
coast. This area of high pressure is forming the southeast side the
atmospheric river. Meanwhile, polar high pressure over the
Aleutians is sending copious Arctic air well to the south through
the North Pacific. This cold air has set up a strong baroclinic
boundary as it runs into the warm air associated with the
subtropical high. Finally, a strong area of low pressure, fed in
part by this same baroclinicity, will move into the British
Columbia coast today. The low and it's trailing cold front moving
into the coast is adding substantial lift to the atmosphere where
the A.R. is located in western Washington. The result of these
various forcings is a "hose" of deep tropical moisture aligned
right into Washington State, then continuing inland through Idaho
and Montana. The low and its front are locally enhancing the rain
rates, especially on the upwind/west-facing slopes of the coastal
ranges and the Cascades. This latest round of heavy rain is coming
after 2+ days of nearly steady rainfall into this same region.
Saturated soils, full rivers, and abundant additional rainfall are
all contributing to flooding concerns through this area.

Heavy rain is likely to continue for much of the day, gradually
diminishing in intensity tonight, but unlikely to stop completely
most anywhere in western Washington. Since the forecast is little
changed, particularly with expected rainfall amounts, the Slight
Risk area is also little changed. A higher end Slight remains in
effect for portions of the western slopes of the Cascades. Very
high snow levels between 8,500 and 9,000 ft are keeping all but the northernmost Cascades as rain. A wedge of colder air trapped in the
northern Cascades are locally keeping snow levels there down closer
to 6,500-7,000 ft. The higher end Slight includes much of the I-90
corridor between Seattle and Snoqualmie Pass. Land and rockslides
remain a concern, and numerous Flood Warnings remain in effect for
much of the western slopes of the Cascades.

...Northern Idaho and Far Western Montana...

The Slight Risk of excessive rainfall also remains in effect for
much of the northern Idaho Panhandle. This includes the I-90
corridor roughly between Coeur d'Alene on the west side to Missoula
on the east side. The strong atmospheric river moving in from the
Pacific will drop the lion's share of its moisture into the coastal
ranges and Cascades. However, plentiful leftover moisture will then
continue east and be re-lifted into the Bitterroots of Idaho and
Montana. While rainfall amounts will be tempered greatly compared
to areas further west, they will still be significantly impactful
for this region, especially when considering it's been raining
off-and-on in this region from this same atmospheric river for the
past 48-72 hours. Thus, soils are saturated and rivers are already
running high in this area. All additional rainfall will convert to
runoff, both worsening and prolonging any resultant flooding
impacts. The area south of I-90 and east of Lewiston with west-
facing slopes will be hardest hit. It is in this area that a higher
end Slight remains in effect.=20

The heaviest rain across this region will be through the day today,
with some modest diminishing of rainfall rates through tonight.
Regardless, most upslope areas should see steady rainfall
throughout this period.=20

Wegman

Day 2
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
NORTHERN IDAHO...

...Northern Idaho...

Thursday will be the final day of the atmospheric river across all
of the Pacific Northwest, including into Idaho. A fast moving
shortwave trough diving southeast in the jet streak will
reinvigorate the heavy rain across northern Idaho and western
Montana during the day Thursday. This shortwave will also usher in
an Arctic front to the east of the Rockies across much of the rest
of Montana. This much colder and drier air will finally allow
conditions to dry out as upper level ridging shoves what's left of
the A.R. northward into Canada, and a large low well out over the
Pacific cuts off the tropical feed as it moves towards Alaska. The
ceasing of tropical moisture will effectively end the heavy rain
threat everywhere, though lingering flooding is likely to continue
in this area for multiple days to come.=20

Heavy rain will likely be ongoing across northern Idaho at the
start of the period on Thursday morning. A surface low will form
along the advancing Arctic air, which will draw the Arctic front
south across much of Montana Thursday night, turning what moisture
is left over to snow east of the range, while putting northern
Idaho into the "dry slot", ending the heavy rainfall. While rain
rates may stay elevated for much of the day Thursday across
northern Idaho, the Slight Risk is at least equally for the ongoing
impacts going into the period from the heavy rain that is likely to
occur tonight. Rock and mudslides will remain a threat until
conditions begin to dry out Thursday night, as well as a
continuation of both ongoing flooding and potentially some new
flooding as the rain ends across the area.

...Western Washington...

A Marginal Risk remains in place across portions of Western
Washington, specifically the foothills of the Cascades on Thursday.
The Marginal Risk reflects the end of the heavy rainfall from the
A.R. from Wednesday and Wednesday night...i.e. diminishing rainfall
rates...and the likely much higher impacts that will be ongoing by
then along all of the Washington Cascades. Thus, expect Slight
level impacts over this corridor to continue, but the heavy rain
ending should spell the end of new or worsening impacts going
forward. The Marginal attempts to strike a balance between these
two competing concerns.

Meteorologically, the A.R. will still be in full swing at the start
of the period 12Z Thursday, but as the forcings from inland lows,
rapidly weakening westerly flow orthogonal to the ranges, and
surface high pressure builds in from the south, rain rates will
rapidly diminish through the morning, ending entirely for many
areas of western Washington by Thursday night. Since the tropical
flow responsible for the A.R. will be cut off by Thursday night,
this will be the end of the event for the area, and a much needed
and "mostly" dry period of weather will follow across most of
western Washington, and those areas that do see additional rain
into the weekend will find it will be a fraction of the intensity
that this A.R. produced, and should be essentially non-impactful.=20

Wegman

Day 3
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_YfyAo0OJ2BkiXnw9JHmGbYkyINKLxAxi8nIYf6WgAER= X1JQoz1XdJN5uJNhDcUNETOQX1eTe6ypuWr94iIwy2dfiz4$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_YfyAo0OJ2BkiXnw9JHmGbYkyINKLxAxi8nIYf6WgAER= X1JQoz1XdJN5uJNhDcUNETOQX1eTe6ypuWr94iIwV1wvoBU$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_YfyAo0OJ2BkiXnw9JHmGbYkyINKLxAxi8nIYf6WgAER= X1JQoz1XdJN5uJNhDcUNETOQX1eTe6ypuWr94iIwcbVZHqI$=20

=3D =3D =3D
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FOUS30 KWBC 101542
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1042 AM EST Wed Dec 10 2025

Day 1
Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF WESTERN
WASHINGTON AS WELL AS FOR PORTIONS OF NORTHERN IDAHO AND FAR
WESTERN MONTANA...


16z update...
Prior discussion/thinking remains on track with respect to
magnitude, timing and placement to the rainfall forecast over
western Washington and downstream into the northern Rockies of
ID/W MT. The core/peak of the AR is currently ongoing and is
expected through 00z with 800-900 kg/m/s of fairly orthogonal
unidirectional flow through depth. After 00z, values will decrease
to 500-600 J/kg but persist through the remainder of the forecast
period, 11.12z.


Major to Record riverine flooding is expected/ongoing across the=20
western slopes of the Washington Cascades, yet rates remain between
.25-.5" with only very highest orthogonal (westward) facing peaks=20
having the potential of an hour or two reaching 2/3rds to .75"/hr.=20 Additional 3-5" for the foothills to peaks (perhaps 6"+) of the=20 Olympics/Washington Cascades over the next few hours. Recent NASA=20
SPoRT LIS 0-40cm soil saturations are over 90% and well into the=20
80-90th percentiles which is very impressive given the time of year
is naturally high. As such, the additional rainfall is almost=20
completely going to run- off further swelling the flooded river and
potential for landslides continues to increase.

Downstream, the IVT values are steadily increasing from 250
currently toward 500 kg/m/s after 00z, while also shifting=20
northward from the Bitterroot/Clearwater Range centering just south
of the Canadian border toward the end of the forecast. With less
overall moisture mainly filtering through the Columbia river and
Plateau of E WA, rates from orographic ascent will be lighter
reaching .10-.25" with peaks near .33". As such, additional totals
of 2-3" are possible. Soil saturation are also well above normal
(99th percentile) and over 70-80% suggesting solid run-off and
rivine flooding concerns to continue here as well too.=20

Given the higher confidence in placement/timing, only small=20
adjustments were required to the current Day 1 categorical areas.=20

Gallina


~~~~Prior Discussion~~~~

...Western Washington...

An atmospheric river is currently impacting much of Washington
State this morning. The narrow but intense plume of deep tropical
moisture originating from near Hawaii is being drawn northeastward
by a strong subtropical high that is parked off the California
coast. This area of high pressure is forming the southeast side the
atmospheric river. Meanwhile, polar high pressure over the
Aleutians is sending copious Arctic air well to the south through
the North Pacific. This cold air has set up a strong baroclinic
boundary as it runs into the warm air associated with the
subtropical high. Finally, a strong area of low pressure, fed in
part by this same baroclinicity, will move into the British
Columbia coast today. The low and it's trailing cold front moving
into the coast is adding substantial lift to the atmosphere where
the A.R. is located in western Washington. The result of these
various forcings is a "hose" of deep tropical moisture aligned
right into Washington State, then continuing inland through Idaho
and Montana. The low and its front are locally enhancing the rain
rates, especially on the upwind/west-facing slopes of the coastal
ranges and the Cascades. This latest round of heavy rain is coming
after 2+ days of nearly steady rainfall into this same region.
Saturated soils, full rivers, and abundant additional rainfall are
all contributing to flooding concerns through this area.

Heavy rain is likely to continue for much of the day, gradually
diminishing in intensity tonight, but unlikely to stop completely
most anywhere in western Washington. Since the forecast is little
changed, particularly with expected rainfall amounts, the Slight
Risk area is also little changed. A higher end Slight remains in
effect for portions of the western slopes of the Cascades. Very
high snow levels between 8,500 and 9,000 ft are keeping all but the northernmost Cascades as rain. A wedge of colder air trapped in the
northern Cascades are locally keeping snow levels there down closer
to 6,500-7,000 ft. The higher end Slight includes much of the I-90
corridor between Seattle and Snoqualmie Pass. Land and rockslides
remain a concern, and numerous Flood Warnings remain in effect for
much of the western slopes of the Cascades.

...Northern Idaho and Far Western Montana...

The Slight Risk of excessive rainfall also remains in effect for
much of the northern Idaho Panhandle. This includes the I-90
corridor roughly between Coeur d'Alene on the west side to Missoula
on the east side. The strong atmospheric river moving in from the
Pacific will drop the lion's share of its moisture into the coastal
ranges and Cascades. However, plentiful leftover moisture will then
continue east and be re-lifted into the Bitterroots of Idaho and
Montana. While rainfall amounts will be tempered greatly compared
to areas further west, they will still be significantly impactful
for this region, especially when considering it's been raining
off-and-on in this region from this same atmospheric river for the
past 48-72 hours. Thus, soils are saturated and rivers are already
running high in this area. All additional rainfall will convert to
runoff, both worsening and prolonging any resultant flooding
impacts. The area south of I-90 and east of Lewiston with west-
facing slopes will be hardest hit. It is in this area that a higher
end Slight remains in effect.

The heaviest rain across this region will be through the day today,
with some modest diminishing of rainfall rates through tonight.
Regardless, most upslope areas should see steady rainfall
throughout this period.

Wegman

Day 2
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
NORTHERN IDAHO...

...Northern Idaho...

Thursday will be the final day of the atmospheric river across all
of the Pacific Northwest, including into Idaho. A fast moving
shortwave trough diving southeast in the jet streak will
reinvigorate the heavy rain across northern Idaho and western
Montana during the day Thursday. This shortwave will also usher in
an Arctic front to the east of the Rockies across much of the rest
of Montana. This much colder and drier air will finally allow
conditions to dry out as upper level ridging shoves what's left of
the A.R. northward into Canada, and a large low well out over the
Pacific cuts off the tropical feed as it moves towards Alaska. The
ceasing of tropical moisture will effectively end the heavy rain
threat everywhere, though lingering flooding is likely to continue
in this area for multiple days to come.

Heavy rain will likely be ongoing across northern Idaho at the
start of the period on Thursday morning. A surface low will form
along the advancing Arctic air, which will draw the Arctic front
south across much of Montana Thursday night, turning what moisture
is left over to snow east of the range, while putting northern
Idaho into the "dry slot", ending the heavy rainfall. While rain
rates may stay elevated for much of the day Thursday across
northern Idaho, the Slight Risk is at least equally for the ongoing
impacts going into the period from the heavy rain that is likely to
occur tonight. Rock and mudslides will remain a threat until
conditions begin to dry out Thursday night, as well as a
continuation of both ongoing flooding and potentially some new
flooding as the rain ends across the area.

...Western Washington...

A Marginal Risk remains in place across portions of Western
Washington, specifically the foothills of the Cascades on Thursday.
The Marginal Risk reflects the end of the heavy rainfall from the
A.R. from Wednesday and Wednesday night...i.e. diminishing rainfall
rates...and the likely much higher impacts that will be ongoing by
then along all of the Washington Cascades. Thus, expect Slight
level impacts over this corridor to continue, but the heavy rain
ending should spell the end of new or worsening impacts going
forward. The Marginal attempts to strike a balance between these
two competing concerns.

Meteorologically, the A.R. will still be in full swing at the start
of the period 12Z Thursday, but as the forcings from inland lows,
rapidly weakening westerly flow orthogonal to the ranges, and
surface high pressure builds in from the south, rain rates will
rapidly diminish through the morning, ending entirely for many
areas of western Washington by Thursday night. Since the tropical
flow responsible for the A.R. will be cut off by Thursday night,
this will be the end of the event for the area, and a much needed
and "mostly" dry period of weather will follow across most of
western Washington, and those areas that do see additional rain
into the weekend will find it will be a fraction of the intensity
that this A.R. produced, and should be essentially non-impactful.

Wegman

Day 3
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7DHz6h4GMxlOUFnNr7fBQH1FLZqiE_EL0tn3ophRivKv= oFvzAFISI7l74LO3Zq03YF5yJ6_puwNb4cZSmcCJWdFzJmY$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7DHz6h4GMxlOUFnNr7fBQH1FLZqiE_EL0tn3ophRivKv= oFvzAFISI7l74LO3Zq03YF5yJ6_puwNb4cZSmcCJQKF5PHo$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7DHz6h4GMxlOUFnNr7fBQH1FLZqiE_EL0tn3ophRivKv= oFvzAFISI7l74LO3Zq03YF5yJ6_puwNb4cZSmcCJNEUG9D0$=20

=3D =3D =3D
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FOUS30 KWBC 101923
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
223 PM EST Wed Dec 10 2025

Day 1
Valid 16Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF WESTERN
WASHINGTON AS WELL AS FOR PORTIONS OF NORTHERN IDAHO AND FAR
WESTERN MONTANA...


16z update...
Prior discussion/thinking remains on track with respect to
magnitude, timing and placement to the rainfall forecast over
western Washington and downstream into the northern Rockies of
ID/W MT. The core/peak of the AR is currently ongoing and is
expected through 00z with 800-900 kg/m/s of fairly orthogonal
unidirectional flow through depth. After 00z, values will decrease
to 500-600 J/kg but persist through the remainder of the forecast
period, 11.12z.


Major to Record riverine flooding is expected/ongoing across the
western slopes of the Washington Cascades, yet rates remain between
.25-.5" with only very highest orthogonal (westward) facing peaks
having the potential of an hour or two reaching 2/3rds to .75"/hr.
Additional 3-5" for the foothills to peaks (perhaps 6"+) of the Olympics/Washington Cascades over the next few hours. Recent NASA
SPoRT LIS 0-40cm soil saturations are over 90% and well into the
80-90th percentiles which is very impressive given the time of year
is naturally high. As such, the additional rainfall is almost
completely going to run- off further swelling the flooded river and
potential for landslides continues to increase.

Downstream, the IVT values are steadily increasing from 250
currently toward 500 kg/m/s after 00z, while also shifting
northward from the Bitterroot/Clearwater Range centering just south
of the Canadian border toward the end of the forecast. With less
overall moisture mainly filtering through the Columbia river and
Plateau of E WA, rates from orographic ascent will be lighter
reaching .10-.25" with peaks near .33". As such, additional totals
of 2-3" are possible. Soil saturation are also well above normal
(99th percentile) and over 70-80% suggesting solid run-off and
rivine flooding concerns to continue here as well too.

Given the higher confidence in placement/timing, only small
adjustments were required to the current Day 1 categorical areas.

Gallina


~~~~Prior Discussion~~~~

...Western Washington...

An atmospheric river is currently impacting much of Washington
State this morning. The narrow but intense plume of deep tropical
moisture originating from near Hawaii is being drawn northeastward
by a strong subtropical high that is parked off the California
coast. This area of high pressure is forming the southeast side the
atmospheric river. Meanwhile, polar high pressure over the
Aleutians is sending copious Arctic air well to the south through
the North Pacific. This cold air has set up a strong baroclinic
boundary as it runs into the warm air associated with the
subtropical high. Finally, a strong area of low pressure, fed in
part by this same baroclinicity, will move into the British
Columbia coast today. The low and it's trailing cold front moving
into the coast is adding substantial lift to the atmosphere where
the A.R. is located in western Washington. The result of these
various forcings is a "hose" of deep tropical moisture aligned
right into Washington State, then continuing inland through Idaho
and Montana. The low and its front are locally enhancing the rain
rates, especially on the upwind/west-facing slopes of the coastal
ranges and the Cascades. This latest round of heavy rain is coming
after 2+ days of nearly steady rainfall into this same region.
Saturated soils, full rivers, and abundant additional rainfall are
all contributing to flooding concerns through this area.

Heavy rain is likely to continue for much of the day, gradually
diminishing in intensity tonight, but unlikely to stop completely
most anywhere in western Washington. Since the forecast is little
changed, particularly with expected rainfall amounts, the Slight
Risk area is also little changed. A higher end Slight remains in
effect for portions of the western slopes of the Cascades. Very
high snow levels between 8,500 and 9,000 ft are keeping all but the northernmost Cascades as rain. A wedge of colder air trapped in the
northern Cascades are locally keeping snow levels there down closer
to 6,500-7,000 ft. The higher end Slight includes much of the I-90
corridor between Seattle and Snoqualmie Pass. Land and rockslides
remain a concern, and numerous Flood Warnings remain in effect for
much of the western slopes of the Cascades.

...Northern Idaho and Far Western Montana...

The Slight Risk of excessive rainfall also remains in effect for
much of the northern Idaho Panhandle. This includes the I-90
corridor roughly between Coeur d'Alene on the west side to Missoula
on the east side. The strong atmospheric river moving in from the
Pacific will drop the lion's share of its moisture into the coastal
ranges and Cascades. However, plentiful leftover moisture will then
continue east and be re-lifted into the Bitterroots of Idaho and
Montana. While rainfall amounts will be tempered greatly compared
to areas further west, they will still be significantly impactful
for this region, especially when considering it's been raining
off-and-on in this region from this same atmospheric river for the
past 48-72 hours. Thus, soils are saturated and rivers are already
running high in this area. All additional rainfall will convert to
runoff, both worsening and prolonging any resultant flooding
impacts. The area south of I-90 and east of Lewiston with west-
facing slopes will be hardest hit. It is in this area that a higher
end Slight remains in effect.

The heaviest rain across this region will be through the day today,
with some modest diminishing of rainfall rates through tonight.
Regardless, most upslope areas should see steady rainfall
throughout this period.

Wegman


Day 2
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
NORTHERN IDAHO...

...Northern Idaho...

Thursday will be the final day of the atmospheric river across all
of the Pacific Northwest, including into Idaho. A fast moving
shortwave trough diving southeast in the jet streak will
reinvigorate the heavy rain across northern Idaho and western
Montana during the day Thursday. This shortwave will also usher in
an Arctic front to the east of the Rockies across much of the rest
of Montana. This much colder and drier air will finally allow
conditions to dry out as upper level ridging shoves what's left of
the A.R. northward into Canada, and a large low well out over the
Pacific cuts off the tropical feed as it moves towards Alaska. The
ceasing of tropical moisture will effectively end the heavy rain
threat everywhere, though lingering flooding is likely to continue
in this area for multiple days to come.

Heavy rain will likely be ongoing across northern Idaho at the
start of the period on Thursday morning. A surface low will form
along the advancing Arctic air, which will draw the Arctic front
south across much of Montana Thursday night, turning what moisture
is left over to snow east of the range, while putting northern
Idaho into the "dry slot", ending the heavy rainfall. While rain
rates may stay elevated for much of the day Thursday across
northern Idaho, the Slight Risk is at least equally for the ongoing
impacts going into the period from the heavy rain that is likely to
occur tonight. Rock and mudslides will remain a threat until
conditions begin to dry out Thursday night, as well as a
continuation of both ongoing flooding and potentially some new
flooding as the rain ends across the area.

...Western Washington...

A Marginal Risk remains in place across portions of Western
Washington, specifically the foothills of the Cascades on Thursday.
The Marginal Risk reflects the end of the heavy rainfall from the
A.R. from Wednesday and Wednesday night...i.e. diminishing rainfall
rates...and the likely much higher impacts that will be ongoing by
then along all of the Washington Cascades. Thus, expect Slight
level impacts over this corridor to continue, but the heavy rain
ending should spell the end of new or worsening impacts going
forward. The Marginal attempts to strike a balance between these
two competing concerns.

Meteorologically, the A.R. will still be in full swing at the start
of the period 12Z Thursday, but as the forcings from inland lows,
rapidly weakening westerly flow orthogonal to the ranges, and
surface high pressure builds in from the south, rain rates will
rapidly diminish through the morning, ending entirely for many
areas of western Washington by Thursday night. Since the tropical
flow responsible for the A.R. will be cut off by Thursday night,
this will be the end of the event for the area, and a much needed
and "mostly" dry period of weather will follow across most of
western Washington, and those areas that do see additional rain
into the weekend will find it will be a fraction of the intensity
that this A.R. produced, and should be essentially non-impactful.

Wegman

Day 3
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6imi9q6nm3rjMRItEeOgUot1J9ZSauYJXVroK1YA51QK= jd44NHid9ko5tomn5wgy8mRAO4Nl5mVvbZTziXCx_n_07HY$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6imi9q6nm3rjMRItEeOgUot1J9ZSauYJXVroK1YA51QK= jd44NHid9ko5tomn5wgy8mRAO4Nl5mVvbZTziXCxBPOhkYs$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6imi9q6nm3rjMRItEeOgUot1J9ZSauYJXVroK1YA51QK= jd44NHid9ko5tomn5wgy8mRAO4Nl5mVvbZTziXCxrAXRJdk$=20

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FOUS30 KWBC 110100
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
800 PM EST Wed Dec 10 2025

Day 1
Valid 01Z Thu Dec 11 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF WESTERN
WASHINGTON AS WELL AS FOR PORTIONS OF NORTHERN IDAHO AND FAR
WESTERN MONTANA...

...01Z update...

The ongoing atmospheric river has resulted in a number of impacts
including several rivers in moderate to major flood stage and
landslides/debris flows across the Washington Cascades. The axis=20
of highest IVT will remain oriented roughly west to east across=20
Washington tonight with peak values in the 600-800 kg/m/s range=20
through 12Z Thursday. While some modest weakening is anticipated as
a mid-leve shortwave advances downstream/southeastward from coastal
British Columbia, and ridging begins to build offshore in the
eastern Pacific, steady moderate to heavy rainfall will continue
through the night. Rain rates should stay below 0.5 in/hr for the
most part, but occasional rates up to 0.7 or 0.8 in/hr cannot be=20
ruled out. 12 hour rainfall totals peaking in the 3 to 5 inch range
are expected for the Washington Cascades and portions of the=20
Olympic Peninsula.

Otto


16z update...
Prior discussion/thinking remains on track with respect to
magnitude, timing and placement to the rainfall forecast over
western Washington and downstream into the northern Rockies of
ID/W MT. The core/peak of the AR is currently ongoing and is
expected through 00z with 800-900 kg/m/s of fairly orthogonal
unidirectional flow through depth. After 00z, values will decrease
to 500-600 J/kg but persist through the remainder of the forecast
period, 11.12z.


Major to Record riverine flooding is expected/ongoing across the
western slopes of the Washington Cascades, yet rates remain between
.25-.5" with only very highest orthogonal (westward) facing peaks
having the potential of an hour or two reaching 2/3rds to .75"/hr.
Additional 3-5" for the foothills to peaks (perhaps 6"+) of the Olympics/Washington Cascades over the next few hours. Recent NASA
SPoRT LIS 0-40cm soil saturations are over 90% and well into the
80-90th percentiles which is very impressive given the time of year
is naturally high. As such, the additional rainfall is almost
completely going to run- off further swelling the flooded river and
potential for landslides continues to increase.

Downstream, the IVT values are steadily increasing from 250
currently toward 500 kg/m/s after 00z, while also shifting
northward from the Bitterroot/Clearwater Range centering just south
of the Canadian border toward the end of the forecast. With less
overall moisture mainly filtering through the Columbia river and
Plateau of E WA, rates from orographic ascent will be lighter
reaching .10-.25" with peaks near .33". As such, additional totals
of 2-3" are possible. Soil saturation are also well above normal
(99th percentile) and over 70-80% suggesting solid run-off and
rivine flooding concerns to continue here as well too.

Given the higher confidence in placement/timing, only small
adjustments were required to the current Day 1 categorical areas.

Gallina


~~~~Prior Discussion~~~~

...Western Washington...

An atmospheric river is currently impacting much of Washington
State this morning. The narrow but intense plume of deep tropical
moisture originating from near Hawaii is being drawn northeastward
by a strong subtropical high that is parked off the California
coast. This area of high pressure is forming the southeast side the
atmospheric river. Meanwhile, polar high pressure over the
Aleutians is sending copious Arctic air well to the south through
the North Pacific. This cold air has set up a strong baroclinic
boundary as it runs into the warm air associated with the
subtropical high. Finally, a strong area of low pressure, fed in
part by this same baroclinicity, will move into the British
Columbia coast today. The low and it's trailing cold front moving
into the coast is adding substantial lift to the atmosphere where
the A.R. is located in western Washington. The result of these
various forcings is a "hose" of deep tropical moisture aligned
right into Washington State, then continuing inland through Idaho
and Montana. The low and its front are locally enhancing the rain
rates, especially on the upwind/west-facing slopes of the coastal
ranges and the Cascades. This latest round of heavy rain is coming
after 2+ days of nearly steady rainfall into this same region.
Saturated soils, full rivers, and abundant additional rainfall are
all contributing to flooding concerns through this area.

Heavy rain is likely to continue for much of the day, gradually
diminishing in intensity tonight, but unlikely to stop completely
most anywhere in western Washington. Since the forecast is little
changed, particularly with expected rainfall amounts, the Slight
Risk area is also little changed. A higher end Slight remains in
effect for portions of the western slopes of the Cascades. Very
high snow levels between 8,500 and 9,000 ft are keeping all but the northernmost Cascades as rain. A wedge of colder air trapped in the
northern Cascades are locally keeping snow levels there down closer
to 6,500-7,000 ft. The higher end Slight includes much of the I-90
corridor between Seattle and Snoqualmie Pass. Land and rockslides
remain a concern, and numerous Flood Warnings remain in effect for
much of the western slopes of the Cascades.

...Northern Idaho and Far Western Montana...

The Slight Risk of excessive rainfall also remains in effect for
much of the northern Idaho Panhandle. This includes the I-90
corridor roughly between Coeur d'Alene on the west side to Missoula
on the east side. The strong atmospheric river moving in from the
Pacific will drop the lion's share of its moisture into the coastal
ranges and Cascades. However, plentiful leftover moisture will then
continue east and be re-lifted into the Bitterroots of Idaho and
Montana. While rainfall amounts will be tempered greatly compared
to areas further west, they will still be significantly impactful
for this region, especially when considering it's been raining
off-and-on in this region from this same atmospheric river for the
past 48-72 hours. Thus, soils are saturated and rivers are already
running high in this area. All additional rainfall will convert to
runoff, both worsening and prolonging any resultant flooding
impacts. The area south of I-90 and east of Lewiston with west-
facing slopes will be hardest hit. It is in this area that a higher
end Slight remains in effect.

The heaviest rain across this region will be through the day today,
with some modest diminishing of rainfall rates through tonight.
Regardless, most upslope areas should see steady rainfall
throughout this period.

Wegman


Day 2
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
NORTHERN IDAHO...

...Northern Idaho...

Thursday will be the final day of the atmospheric river across all
of the Pacific Northwest, including into Idaho. A fast moving
shortwave trough diving southeast in the jet streak will
reinvigorate the heavy rain across northern Idaho and western
Montana during the day Thursday. This shortwave will also usher in
an Arctic front to the east of the Rockies across much of the rest
of Montana. This much colder and drier air will finally allow
conditions to dry out as upper level ridging shoves what's left of
the A.R. northward into Canada, and a large low well out over the
Pacific cuts off the tropical feed as it moves towards Alaska. The
ceasing of tropical moisture will effectively end the heavy rain
threat everywhere, though lingering flooding is likely to continue
in this area for multiple days to come.

Heavy rain will likely be ongoing across northern Idaho at the
start of the period on Thursday morning. A surface low will form
along the advancing Arctic air, which will draw the Arctic front
south across much of Montana Thursday night, turning what moisture
is left over to snow east of the range, while putting northern
Idaho into the "dry slot", ending the heavy rainfall. While rain
rates may stay elevated for much of the day Thursday across
northern Idaho, the Slight Risk is at least equally for the ongoing
impacts going into the period from the heavy rain that is likely to
occur tonight. Rock and mudslides will remain a threat until
conditions begin to dry out Thursday night, as well as a
continuation of both ongoing flooding and potentially some new
flooding as the rain ends across the area.

...Western Washington...

A Marginal Risk remains in place across portions of Western
Washington, specifically the foothills of the Cascades on Thursday.
The Marginal Risk reflects the end of the heavy rainfall from the
A.R. from Wednesday and Wednesday night...i.e. diminishing rainfall
rates...and the likely much higher impacts that will be ongoing by
then along all of the Washington Cascades. Thus, expect Slight
level impacts over this corridor to continue, but the heavy rain
ending should spell the end of new or worsening impacts going
forward. The Marginal attempts to strike a balance between these
two competing concerns.

Meteorologically, the A.R. will still be in full swing at the start
of the period 12Z Thursday, but as the forcings from inland lows,
rapidly weakening westerly flow orthogonal to the ranges, and
surface high pressure builds in from the south, rain rates will
rapidly diminish through the morning, ending entirely for many
areas of western Washington by Thursday night. Since the tropical
flow responsible for the A.R. will be cut off by Thursday night,
this will be the end of the event for the area, and a much needed
and "mostly" dry period of weather will follow across most of
western Washington, and those areas that do see additional rain
into the weekend will find it will be a fraction of the intensity
that this A.R. produced, and should be essentially non-impactful.

Wegman

Day 3
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9tXMhXyJVuxZj9VbKHzS7_Yoac9nrD_PDeh84ToqeHMQ= 7BiPmgz4DjlbAvuho8v3iD7jRqYbsBHNWFd3sZXxwcYlWfw$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9tXMhXyJVuxZj9VbKHzS7_Yoac9nrD_PDeh84ToqeHMQ= 7BiPmgz4DjlbAvuho8v3iD7jRqYbsBHNWFd3sZXxm-k4V6U$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9tXMhXyJVuxZj9VbKHzS7_Yoac9nrD_PDeh84ToqeHMQ= 7BiPmgz4DjlbAvuho8v3iD7jRqYbsBHNWFd3sZXxyJsPiQ0$=20

=3D =3D =3D
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FOUS30 KWBC 110734
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
234 AM EST Thu Dec 11 2025

Day 1
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN WASHINGTON AS WELL AS FOR NORTHERN IDAHO INTO FAR WESTERN=20
MONTANA...

...Western Washington...

The multi-day atmospheric river (A.R.) event of much of the past
week will finally conclude across western Washington today.
Northward-building ridging both at the surface and at the jet=20
stream level will push the remaining moisture plume from the
already weakening A.R. north into Canada, leaving much of western
Washington with residual moisture from the weakening and drying
westerly flow. Heavy rain is ongoing across much of western
Washington, roughly from Tacoma's latitude north. CAMS guidance
shows the rain should progress a bit further south over the next
few hours as a cold front offshore pushes inland. After that it
will stall out, and the rain rates will diminish in place. Thus,
the heaviest rain over the area for this period will be over the
next few hours this morning, followed by tapering through the
afternoon and into tonight.

Record and in some areas historic flooding is ongoing from the
multiple consecutive days of heavy rain with the A.R. Comparatively
speaking, today's rainfall totals won't be anything near previous
days' totals. Nevertheless, the ongoing moderate to heavy rain
across northern Washington will continue to keep river levels up,
or even rising through the morning until rain rates can diminish a
bit. The Marginal Risk therefore is a compromise between the
ongoing highly impactful flooding and steady rain expected to
continue into the morning, and the fact that the second half to
two-thirds of the period should feature only light rain with the
conclusion of the A.R. event. That is to say that for all of the
Marginal Risk area, ongoing major flooding will continue through
today despite the diminishing rain, and precautions and avoidance
of flooded areas should be taken. The Marginal Risk may be able to
be dropped with the evening update.

...Northern Idaho and Far Western Montana...

Continuous steady rain is expected to continue through the entire
period across the Marginal Risk area in northern Idaho and far
western Montana today. While the A.R. is ending out west, it will
take longer to do so for Idaho and Montana as the forcings
supporting the steady rain will persist throughout the period.
Despite the heavy rain on the order of 1-2 inches over the past 24
hours, in addition to the multiple inches that fell in this same
area in days prior, impacts from flooding have been minimal across
this region. Now, with today being the tail end of the A.R., it's
probable that if flooding impacts were to occur, they would happen
today. Thus, balancing these two offsetting factors, and in
coordination with OTX/Spokane, WA forecast office, the inherited
Slight Risk for this region was downgraded. Isolated instances of
flash flooding are still possible given the expectation of another
24 hours or so of steady rain into the west facing slopes of the
Bitterroots. However, given the lack of impacts thus far, it seems
probable that the same trends will continue through tonight. Steady precipitation should taper off soon after the 12Z Friday end time
for the period, as an Arctic air mass further east also works to
transition any remaining rain over to snow.

Wegman

Day 2
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman

Day 3
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4hPK1xNIhvnTohJCD5ygSMyTx-1lVeFCiSHUwRfuliur= fS0KlpqGlp2sH5e3f1gwC4rEpHhqLl2pVVl_IZnH7_U0Eno$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4hPK1xNIhvnTohJCD5ygSMyTx-1lVeFCiSHUwRfuliur= fS0KlpqGlp2sH5e3f1gwC4rEpHhqLl2pVVl_IZnHXsjtjr0$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4hPK1xNIhvnTohJCD5ygSMyTx-1lVeFCiSHUwRfuliur= fS0KlpqGlp2sH5e3f1gwC4rEpHhqLl2pVVl_IZnHsuQGbM0$=20

=3D =3D =3D
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FOUS30 KWBC 111540
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1040 AM EST Thu Dec 11 2025

Day 1
Valid 16Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN WASHINGTON AS WELL AS FOR NORTHERN IDAHO INTO FAR WESTERN
MONTANA...

...16Z Outlook Update...
The ongoing forecast is on track. Refer to Mesoscale Precipitation
Discussion #1262 for shorter-term updates on precipitation/flash
flood threats across western Washington State. Refer to the
discussion below for more details on flood/flash flood potential in
Idaho and Montana today.

Cook

...Previous Discussion...

...Western Washington...

The multi-day atmospheric river (A.R.) event of much of the past
week will finally conclude across western Washington today.
Northward-building ridging both at the surface and at the jet
stream level will push the remaining moisture plume from the
already weakening A.R. north into Canada, leaving much of western
Washington with residual moisture from the weakening and drying
westerly flow. Heavy rain is ongoing across much of western
Washington, roughly from Tacoma's latitude north. CAMS guidance
shows the rain should progress a bit further south over the next
few hours as a cold front offshore pushes inland. After that it
will stall out, and the rain rates will diminish in place. Thus,
the heaviest rain over the area for this period will be over the
next few hours this morning, followed by tapering through the
afternoon and into tonight.

Record and in some areas historic flooding is ongoing from the
multiple consecutive days of heavy rain with the A.R. Comparatively
speaking, today's rainfall totals won't be anything near previous
days' totals. Nevertheless, the ongoing moderate to heavy rain
across northern Washington will continue to keep river levels up,
or even rising through the morning until rain rates can diminish a
bit. The Marginal Risk therefore is a compromise between the
ongoing highly impactful flooding and steady rain expected to
continue into the morning, and the fact that the second half to
two-thirds of the period should feature only light rain with the
conclusion of the A.R. event. That is to say that for all of the
Marginal Risk area, ongoing major flooding will continue through
today despite the diminishing rain, and precautions and avoidance
of flooded areas should be taken. The Marginal Risk may be able to
be dropped with the evening update.

...Northern Idaho and Far Western Montana...

Continuous steady rain is expected to continue through the entire
period across the Marginal Risk area in northern Idaho and far
western Montana today. While the A.R. is ending out west, it will
take longer to do so for Idaho and Montana as the forcings
supporting the steady rain will persist throughout the period.
Despite the heavy rain on the order of 1-2 inches over the past 24
hours, in addition to the multiple inches that fell in this same
area in days prior, impacts from flooding have been minimal across
this region. Now, with today being the tail end of the A.R., it's
probable that if flooding impacts were to occur, they would happen
today. Thus, balancing these two offsetting factors, and in
coordination with OTX/Spokane, WA forecast office, the inherited
Slight Risk for this region was downgraded. Isolated instances of
flash flooding are still possible given the expectation of another
24 hours or so of steady rain into the west facing slopes of the
Bitterroots. However, given the lack of impacts thus far, it seems
probable that the same trends will continue through tonight. Steady precipitation should taper off soon after the 12Z Friday end time
for the period, as an Arctic air mass further east also works to
transition any remaining rain over to snow.

Wegman

Day 2
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman

Day 3
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7rBhq94JwtEik5j7ztY0pOyPCUS1WZfJuOizydDdYTAJ= uk4DXBPBEljRmcSPGB--84qG3QBnHXasWtcMrpOfRQPRwxo$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7rBhq94JwtEik5j7ztY0pOyPCUS1WZfJuOizydDdYTAJ= uk4DXBPBEljRmcSPGB--84qG3QBnHXasWtcMrpOf_VdDb5M$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7rBhq94JwtEik5j7ztY0pOyPCUS1WZfJuOizydDdYTAJ= uk4DXBPBEljRmcSPGB--84qG3QBnHXasWtcMrpOfpk_LSAA$=20

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FOUS30 KWBC 111941
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
241 PM EST Thu Dec 11 2025

Day 1
Valid 16Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN WASHINGTON AS WELL AS FOR NORTHERN IDAHO INTO FAR WESTERN
MONTANA...

...16Z Outlook Update...
The ongoing forecast is on track. Refer to Mesoscale Precipitation
Discussion #1262 for shorter-term updates on precipitation/flash
flood threats across western Washington State. Refer to the
discussion below for more details on flood/flash flood potential in
Idaho and Montana today.

Cook

...Previous Discussion...

...Western Washington...

The multi-day atmospheric river (A.R.) event of much of the past
week will finally conclude across western Washington today.
Northward-building ridging both at the surface and at the jet
stream level will push the remaining moisture plume from the
already weakening A.R. north into Canada, leaving much of western
Washington with residual moisture from the weakening and drying
westerly flow. Heavy rain is ongoing across much of western
Washington, roughly from Tacoma's latitude north. CAMS guidance
shows the rain should progress a bit further south over the next
few hours as a cold front offshore pushes inland. After that it
will stall out, and the rain rates will diminish in place. Thus,
the heaviest rain over the area for this period will be over the
next few hours this morning, followed by tapering through the
afternoon and into tonight.

Record and in some areas historic flooding is ongoing from the
multiple consecutive days of heavy rain with the A.R. Comparatively
speaking, today's rainfall totals won't be anything near previous
days' totals. Nevertheless, the ongoing moderate to heavy rain
across northern Washington will continue to keep river levels up,
or even rising through the morning until rain rates can diminish a
bit. The Marginal Risk therefore is a compromise between the
ongoing highly impactful flooding and steady rain expected to
continue into the morning, and the fact that the second half to
two-thirds of the period should feature only light rain with the
conclusion of the A.R. event. That is to say that for all of the
Marginal Risk area, ongoing major flooding will continue through
today despite the diminishing rain, and precautions and avoidance
of flooded areas should be taken. The Marginal Risk may be able to
be dropped with the evening update.

...Northern Idaho and Far Western Montana...

Continuous steady rain is expected to continue through the entire
period across the Marginal Risk area in northern Idaho and far
western Montana today. While the A.R. is ending out west, it will
take longer to do so for Idaho and Montana as the forcings
supporting the steady rain will persist throughout the period.
Despite the heavy rain on the order of 1-2 inches over the past 24
hours, in addition to the multiple inches that fell in this same
area in days prior, impacts from flooding have been minimal across
this region. Now, with today being the tail end of the A.R., it's
probable that if flooding impacts were to occur, they would happen
today. Thus, balancing these two offsetting factors, and in
coordination with OTX/Spokane, WA forecast office, the inherited
Slight Risk for this region was downgraded. Isolated instances of
flash flooding are still possible given the expectation of another
24 hours or so of steady rain into the west facing slopes of the
Bitterroots. However, given the lack of impacts thus far, it seems
probable that the same trends will continue through tonight. Steady precipitation should taper off soon after the 12Z Friday end time
for the period, as an Arctic air mass further east also works to
transition any remaining rain over to snow.

Wegman

Day 2
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley

Day 3
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6Bu1SSvlVEyItynOdLUR1BFCcOQc99Fo6GimoNDVCVIf= s9M_OzSIIMMOAFDyAmnurPPLHz6q40v05jRT3wxyoGTF8Zc$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6Bu1SSvlVEyItynOdLUR1BFCcOQc99Fo6GimoNDVCVIf= s9M_OzSIIMMOAFDyAmnurPPLHz6q40v05jRT3wxyoXo9vKA$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6Bu1SSvlVEyItynOdLUR1BFCcOQc99Fo6GimoNDVCVIf= s9M_OzSIIMMOAFDyAmnurPPLHz6q40v05jRT3wxyRog4D1Q$=20

=3D =3D =3D
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FOUS30 KWBC 120052
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
752 PM EST Thu Dec 11 2025

Day 1
Valid 01Z Fri Dec 12 2025 - 12Z Fri Dec 12 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN WASHINGTON AS WELL AS FOR NORTHERN IDAHO INTO FAR WESTERN
MONTANA...

...Western Washington...

GOES West water vapor imagery showed ridging off of the West Coast
continuing to amplify downstream of an upper level trough/closed
low near 160 W. The result has been a reduction in precipitable
water values and low level winds along the coast of the Pacific=20
Northwest. IVT values at 00Z ranged from about 250 kg/m/s across=20
western Washington to ~450 kg/m/s across eastern Washington, and=20
these values are forecast to continue lowering through 12Z Friday.

Recent hourly rainfall over the upslope regions of western=20
Washington was generally below 0.10 inches, but isolated pockets of
greater than 0.10 inches in an hour remained across portions of=20
the southern Cascades. As a warm front located along and west of=20
the Washington coastline lifts north tonight, the ongoing moisture=20
axis will also lift north with further weakening of IVT values,=20
keeping rainfall light but steady into the Coastal Ranges and=20
Cascades. Peak additional rainfall totals up to 1 inch (perhaps=20
isolated spots near 1.5 inches) are expected through 12Z.=20

While the expected overnight rainfall shouldn't amount to a
significant contribution to additional flooding, a Marginal Risk=20
was maintained given ongoing major flooding across the region and=20
continued potential for landslides/debris flows within the higher=20
terrain. Precautions and avoidance of flooded areas should be=20
taken.=20

...Northern Idaho and Far Western Montana...

Light to occasionally moderate rainfall is expected to continue
across the northern Rockies of Idaho and Montana overnight.
Westerly flow between 40-50 kt at 700 mb will help contribute to
IVT values initially between 300-450 kg/m/s from eastern=20
Washington downstream across the Rockies, but weakening to near 300
kg/m/s through 12Z. Rainfall intensities should remain light for=20
the most part but pockets of moderate rainfall should be expected=20
overnight and additional peak rainfall totals of 1 to 1.5 inches=20
are expected through 12Z Friday. The Marginal Risk was maintained=20
due to ongoing flooding throughout the region and the potential for
additional impacts, although contributions to ongoing flooding=20
concerns from tonight's rainfall should be minimal.

Otto


Day 2
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 3
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4ahV5l2RDV0xqBfC0zNjTB-mV5FbpKJfh3DzTc4bPChU= 283CWJJ8ncIbzdSoKV59WIc5mGfddlYw_QBHB-Fe9YSh-JM$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4ahV5l2RDV0xqBfC0zNjTB-mV5FbpKJfh3DzTc4bPChU= 283CWJJ8ncIbzdSoKV59WIc5mGfddlYw_QBHB-FegINoCGg$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4ahV5l2RDV0xqBfC0zNjTB-mV5FbpKJfh3DzTc4bPChU= 283CWJJ8ncIbzdSoKV59WIc5mGfddlYw_QBHB-FeD9il2ts$=20

=3D =3D =3D
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FOUS30 KWBC 120826
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
326 AM EST Fri Dec 12 2025

Day 1
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann

Day 2
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann

Day 3
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN WASHINGTON...

Introduced a Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next push of moisture
approaches late Sunday night into the early morning hours of
Monday. Much of the rainfall on Sunday is currently expected to=20
fall north of the international boarder with rainfall in the=20
Pacific Northwest not increasing in coverage or intensity until=20
late in the Day 3 period. The 11/12Z UKMET was most aggressive with
QPF and there were several global models that limited QPF to under
a quarter of an inch. Based on the expected IVT plume increasing=20
to over 600 at about the time that the flow begins to take on an=20
on-shore component...am inclined to follow the ensemble idea of=20
0.75 inches to locally 1.5 inches of precipitation focused in the=20
terrain. The area is sensitive given the nearly week-long soaking=20
so any additional rainfall is expected to bring renewed hydrologic=20
concerns. Given a fairly tight window of opportunity for rainfall=20
in the Day 3 period and at least some prospect that the arrival of=20
higher rainfall rates and amounts will occur after 15/12Z...issued=20
a Marginal Risk for now. Later shifts can adjust if needed.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!41iaBSiBSfLONsrWVi6FPoe3zyjvqEqTP9Jy6cT_3l7r= Tyzvz0owpX244Sv3owln6Ei_fawvC9M-E6YgCwSt3S1ozxE$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!41iaBSiBSfLONsrWVi6FPoe3zyjvqEqTP9Jy6cT_3l7r= Tyzvz0owpX244Sv3owln6Ei_fawvC9M-E6YgCwStrXzRv3c$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!41iaBSiBSfLONsrWVi6FPoe3zyjvqEqTP9Jy6cT_3l7r= Tyzvz0owpX244Sv3owln6Ei_fawvC9M-E6YgCwSt2mX2wDY$=20

=3D =3D =3D
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FOUS30 KWBC 121505
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1005 AM EST Fri Dec 12 2025

Day 1
Valid 16Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Cook/Bann

Day 2
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann

Day 3
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN WASHINGTON...

Introduced a Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next push of moisture
approaches late Sunday night into the early morning hours of
Monday. Much of the rainfall on Sunday is currently expected to
fall north of the international boarder with rainfall in the
Pacific Northwest not increasing in coverage or intensity until
late in the Day 3 period. The 11/12Z UKMET was most aggressive with
QPF and there were several global models that limited QPF to under
a quarter of an inch. Based on the expected IVT plume increasing
to over 600 at about the time that the flow begins to take on an
on-shore component...am inclined to follow the ensemble idea of
0.75 inches to locally 1.5 inches of precipitation focused in the
terrain. The area is sensitive given the nearly week-long soaking
so any additional rainfall is expected to bring renewed hydrologic
concerns. Given a fairly tight window of opportunity for rainfall
in the Day 3 period and at least some prospect that the arrival of
higher rainfall rates and amounts will occur after 15/12Z...issued
a Marginal Risk for now. Later shifts can adjust if needed.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4kOZwgAs_x7Ks9I300JA91O6lY5YEZxbHM_AWtqiw_A2= gPbnaad9I8WeRZfK4GS7VKFqVVSUbx0nPwihZWe2OfZKoU0$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4kOZwgAs_x7Ks9I300JA91O6lY5YEZxbHM_AWtqiw_A2= gPbnaad9I8WeRZfK4GS7VKFqVVSUbx0nPwihZWe21vmR12U$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4kOZwgAs_x7Ks9I300JA91O6lY5YEZxbHM_AWtqiw_A2= gPbnaad9I8WeRZfK4GS7VKFqVVSUbx0nPwihZWe2ZdApmRk$=20

=3D =3D =3D
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FOUS30 KWBC 121922
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
222 PM EST Fri Dec 12 2025

Day 1
Valid 16Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Cook/Bann

Day 2
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann

Day 3
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN WASHINGTON...

...2100 UTC Update: In terms of the guidance, some of the 12Z model
QPFs have come up a bit (GFS and ECMWF), while others have trended
down (CMC and NAM) in western WA across the Olympics and northern=20
Cascades. 12Z UKMet meanwhile was similar to 00Z. Still some timing
differences therefore with the onset of the next (more SW-NE
oriented) AR, with the GFS and ECMWF similar with the faster timing
and thus uptick in heavier QPF late in the period (00-12Z Sun). The
upshot was very minimal changes to the Day 3 Marginal ERO.=20

Hurley

Previous discussion below...

Introduced a Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next push of moisture
approaches late Sunday night into the early morning hours of
Monday. Much of the rainfall on Sunday is currently expected to
fall north of the international boarder with rainfall in the
Pacific Northwest not increasing in coverage or intensity until
late in the Day 3 period. The 11/12Z UKMET was most aggressive with
QPF and there were several global models that limited QPF to under
a quarter of an inch. Based on the expected IVT plume increasing
to over 600 at about the time that the flow begins to take on an
on-shore component...am inclined to follow the ensemble idea of
0.75 inches to locally 1.5 inches of precipitation focused in the
terrain. The area is sensitive given the nearly week-long soaking
so any additional rainfall is expected to bring renewed hydrologic
concerns. Given a fairly tight window of opportunity for rainfall
in the Day 3 period and at least some prospect that the arrival of
higher rainfall rates and amounts will occur after 15/12Z...issued
a Marginal Risk for now. Later shifts can adjust if needed.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7CpRiNQ5BaJ2Zfh_21Q_J54owzMxMfbBYp52dpwrDKA7= kFz7xBcu-17_jq3Vu-CnsvDJ4JiOxwmaoNATTE3Ncsj4MxI$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7CpRiNQ5BaJ2Zfh_21Q_J54owzMxMfbBYp52dpwrDKA7= kFz7xBcu-17_jq3Vu-CnsvDJ4JiOxwmaoNATTE3N5UPL888$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7CpRiNQ5BaJ2Zfh_21Q_J54owzMxMfbBYp52dpwrDKA7= kFz7xBcu-17_jq3Vu-CnsvDJ4JiOxwmaoNATTE3NiFK8IXM$=20

=3D =3D =3D
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FOUS30 KWBC 130033
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
733 PM EST Fri Dec 12 2025

Day 1
Valid 01Z Sat Dec 13 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Otto


Day 2
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 3
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN WASHINGTON...

...2100 UTC Update: In terms of the guidance, some of the 12Z model
QPFs have come up a bit (GFS and ECMWF), while others have trended
down (CMC and NAM) in western WA across the Olympics and northern
Cascades. 12Z UKMet meanwhile was similar to 00Z. Still some timing
differences therefore with the onset of the next (more SW-NE
oriented) AR, with the GFS and ECMWF similar with the faster timing
and thus uptick in heavier QPF late in the period (00-12Z Sun). The
upshot was very minimal changes to the Day 3 Marginal ERO.

Hurley

Previous discussion below...

Introduced a Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next push of moisture
approaches late Sunday night into the early morning hours of
Monday. Much of the rainfall on Sunday is currently expected to
fall north of the international boarder with rainfall in the
Pacific Northwest not increasing in coverage or intensity until
late in the Day 3 period. The 11/12Z UKMET was most aggressive with
QPF and there were several global models that limited QPF to under
a quarter of an inch. Based on the expected IVT plume increasing
to over 600 at about the time that the flow begins to take on an
on-shore component...am inclined to follow the ensemble idea of
0.75 inches to locally 1.5 inches of precipitation focused in the
terrain. The area is sensitive given the nearly week-long soaking
so any additional rainfall is expected to bring renewed hydrologic
concerns. Given a fairly tight window of opportunity for rainfall
in the Day 3 period and at least some prospect that the arrival of
higher rainfall rates and amounts will occur after 15/12Z...issued
a Marginal Risk for now. Later shifts can adjust if needed.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9L9GuUx8PqsvZEiK7mYFFLEW8hb0kRaFkvppjHzpiNrG= xw3D4_Hpnl2nsUdYbSe8NSgpCRw41SCfcLNlnNjD8caC-80$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9L9GuUx8PqsvZEiK7mYFFLEW8hb0kRaFkvppjHzpiNrG= xw3D4_Hpnl2nsUdYbSe8NSgpCRw41SCfcLNlnNjD1MIzHgI$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9L9GuUx8PqsvZEiK7mYFFLEW8hb0kRaFkvppjHzpiNrG= xw3D4_Hpnl2nsUdYbSe8NSgpCRw41SCfcLNlnNjDmt_gyLg$=20

=3D =3D =3D
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FOUS30 KWBC 130824
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
324 AM EST Sat Dec 13 2025

Day 1
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.=20

Bann


Day 2
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

..THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF=20
WESTERN WASHINGTON STATE LATE SUNDAY NIGHT/EARLY MONDAY MORNING...

Maintained the Marginal Risk area over parts of the Olympic and=20
northern Cascade Ranges in Washington as the next push of moisture=20 approaches late Sunday night into the early morning hours of=20
Monday. The models have shown some run to run differences with QPF=20
but no real clear trend. One consistent signal is that the=20
orientation of the moisture plume remained more southwest-northeast
than the event that just ended a couple of days ago. That still=20
points to the idea that rainfall may not increase in coverage or=20
intensity until late in the Day 2 period. Based on the expected IVT
plume increasing to over 600 at about the time that the flow=20
reaches the coast and begins to take on more of an on- shore=20
component...am inclined to follow the ensemble idea of 0.75 inches=20
to locally 1.5 inches of precipitation focused in the terrain. The=20
area is sensitive given the nearly week-long excessive rainfall=20
event...so any additional rainfall is expected to bring renewed=20
hydrologic concerns. Given a fairly tight window of opportunity for
rainfall during the outlook period...and at least some questions=20
about timing of the onset....still think a Marginal Risk is=20
sufficient for now although later shifts can adjust if needed.

Bann

Day 3
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
WASHINGTON AND OREGON...

Areal coverage of rainfall expands and rainrates increase on Monday
as a well defined atmospheric river continues to direct abundant
moisture into the Washington coastal ranges and Cascades that
gradually makes its way southward into Oregon. Given antecedent
conditions from the excessive rainfall event from earlier in the
week plus whatever falls on Day 2...the concern is for renewed
flooding potential in addition to worsening on-going flooding=20
especially in the terrain with potential for additional landslides=20
or mudslides. Saw little reason to modify the Slight risk area that
propagated into the Day 3 period from yesterdays Day 4 outlook=20
especially given the magnitude of the IVT and precipitable water=20
values forecast by the global models. The focus of the heavy=20
rainfall should gradually shift southward into an area that did not
receive as much rainfall from the previous atmospheric river.=20
Opted to extend a Marginal risk area along the coast as far south=20
as northwestern California more in deference to uncertainty of=20
timing as to the rainfall amounts.=20

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!68aCra7KzTwu5f99YQRkb4cpHCppbxCCpUto982064dk= nbXyGawvgicsKtRcPjWVSq14iL7lRekFYm2LAOD9YB5A69Q$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!68aCra7KzTwu5f99YQRkb4cpHCppbxCCpUto982064dk= nbXyGawvgicsKtRcPjWVSq14iL7lRekFYm2LAOD959R9D5E$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!68aCra7KzTwu5f99YQRkb4cpHCppbxCCpUto982064dk= nbXyGawvgicsKtRcPjWVSq14iL7lRekFYm2LAOD94ZveedA$=20

=3D =3D =3D
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FOUS30 KWBC 131501
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1001 AM EST Sat Dec 13 2025

Day 1
Valid 16Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
SOUTHEASTERN FLORIDA...

A weak mid-level wave over the eastern Gulf will aid in increasing
mid-level flow/ascent across the Florida Peninsula and adjacent=20
Gulf Stream during the overnight hours. Meanwhile, low-level=20
moisture will increase across coastal areas as a weak surface=20 boundary/inverted trough becomes established just inland across the
Peninsula. PW values should increse into the 1.6-1.8 inch range=20
amid 500+ J/kg SBCAPE. Meanwhile, point forecast soundings depict=20
favorable kinematic profiles for relatively slow-moving cells that=20
could impact urban areas of southeast Florida along the I-95=20
corridor. Local 1+ inch/hr rates are possible. Urban flash flooding
is possible in the 03-12Z timeframe this evening/tonight.

Cook

Day 2
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

..THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN WASHINGTON STATE LATE SUNDAY NIGHT/EARLY MONDAY MORNING...

Maintained the Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next push of moisture
approaches late Sunday night into the early morning hours of
Monday. The models have shown some run to run differences with QPF
but no real clear trend. One consistent signal is that the
orientation of the moisture plume remained more southwest-northeast
than the event that just ended a couple of days ago. That still
points to the idea that rainfall may not increase in coverage or
intensity until late in the Day 2 period. Based on the expected IVT
plume increasing to over 600 at about the time that the flow
reaches the coast and begins to take on more of an on- shore
component...am inclined to follow the ensemble idea of 0.75 inches
to locally 1.5 inches of precipitation focused in the terrain. The
area is sensitive given the nearly week-long excessive rainfall
event...so any additional rainfall is expected to bring renewed
hydrologic concerns. Given a fairly tight window of opportunity for
rainfall during the outlook period...and at least some questions
about timing of the onset....still think a Marginal Risk is
sufficient for now although later shifts can adjust if needed.

Bann

Day 3
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
WASHINGTON AND OREGON...

Areal coverage of rainfall expands and rainrates increase on Monday
as a well defined atmospheric river continues to direct abundant
moisture into the Washington coastal ranges and Cascades that
gradually makes its way southward into Oregon. Given antecedent
conditions from the excessive rainfall event from earlier in the
week plus whatever falls on Day 2...the concern is for renewed
flooding potential in addition to worsening on-going flooding
especially in the terrain with potential for additional landslides
or mudslides. Saw little reason to modify the Slight risk area that
propagated into the Day 3 period from yesterdays Day 4 outlook
especially given the magnitude of the IVT and precipitable water
values forecast by the global models. The focus of the heavy
rainfall should gradually shift southward into an area that did not
receive as much rainfall from the previous atmospheric river.
Opted to extend a Marginal risk area along the coast as far south
as northwestern California more in deference to uncertainty of
timing as to the rainfall amounts.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8g954PfN3kpfoI-InQgq2iyZB0Rl7sdQy4Ee1cc72gpy= iTjRbkOMihiyCSs6MwsyqQHfnoak3bcQgcE1GAkuoqXbMcE$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8g954PfN3kpfoI-InQgq2iyZB0Rl7sdQy4Ee1cc72gpy= iTjRbkOMihiyCSs6MwsyqQHfnoak3bcQgcE1GAkumbpuYA0$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8g954PfN3kpfoI-InQgq2iyZB0Rl7sdQy4Ee1cc72gpy= iTjRbkOMihiyCSs6MwsyqQHfnoak3bcQgcE1GAkug_RdmXg$=20

=3D =3D =3D
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FOUS30 KWBC 131950
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
250 PM EST Sat Dec 13 2025

Day 1
Valid 16Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
SOUTHEASTERN FLORIDA...

A weak mid-level wave over the eastern Gulf will aid in increasing
mid-level flow/ascent across the Florida Peninsula and adjacent
Gulf Stream during the overnight hours. Meanwhile, low-level
moisture will increase across coastal areas as a weak surface
boundary/inverted trough becomes established just inland across the
Peninsula. PW values should increase into the 1.6-1.8 inch range
amid 500+ J/kg SBCAPE. Meanwhile, point forecast soundings depict
favorable kinematic profiles for relatively slow-moving cells that
could impact urban areas of southeast Florida along the I-95
corridor. Local 1+ inch/hr rates are possible. Urban flash flooding
is possible in the 03-12Z timeframe this evening/tonight.

Cook

Day 2
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

..THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN WASHINGTON STATE LATE SUNDAY NIGHT/EARLY MONDAY MORNING...

2100 UTC Update -- No changes made to the Marginal Risk outlook
based on the new (12Z) guidance. 12Z HREF window runs through the
entire D2 period, and of note is the uptick in 0.50"/hr
probabilities after 06Z -- peaking over 80% across the Olympic
Ranges toward 12Z Mon, and over 40% across portions of the Cascades
in WA.

Hurley

Previous discussion...

Maintained the Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next push of moisture
approaches late Sunday night into the early morning hours of
Monday. The models have shown some run to run differences with QPF
but no real clear trend. One consistent signal is that the
orientation of the moisture plume remained more southwest-northeast
than the event that just ended a couple of days ago. That still
points to the idea that rainfall may not increase in coverage or
intensity until late in the Day 2 period. Based on the expected IVT
plume increasing to over 600 at about the time that the flow
reaches the coast and begins to take on more of an on- shore
component...am inclined to follow the ensemble idea of 0.75 inches
to locally 1.5 inches of precipitation focused in the terrain. The
area is sensitive given the nearly week-long excessive rainfall
event...so any additional rainfall is expected to bring renewed
hydrologic concerns. Given a fairly tight window of opportunity for
rainfall during the outlook period...and at least some questions
about timing of the onset....still think a Marginal Risk is
sufficient for now although later shifts can adjust if needed.

Bann

Day 3
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
WASHINGTON AND OREGON...

2100 UTC Update -- Only minor (cosmetic) changes made to the=20
previous D3 outlook, some of which was to pull the eastern edges of
the Slight ever so slightly westward in WA based on the latest=20
snowfall forecast (lowering snow levels).

Hurley

Previous discussion...

Areal coverage of rainfall expands and rain rates increase on=20
Monday as a well defined atmospheric river continues to direct=20
abundant moisture into the Washington coastal ranges and Cascades=20
that gradually makes its way southward into Oregon. Given=20
antecedent conditions from the excessive rainfall event from=20
earlier in the week plus whatever falls on Day 2...the concern is=20
for renewed flooding potential in addition to worsening on-going=20
flooding especially in the terrain with potential for additional=20
landslides or mudslides. Saw little reason to modify the Slight=20
risk area that propagated into the Day 3 period from yesterdays Day
4 outlook especially given the magnitude of the IVT and=20
precipitable water values forecast by the global models. The focus=20
of the heavy rainfall should gradually shift southward into an area
that did not receive as much rainfall from the previous=20
atmospheric river. Opted to extend a Marginal risk area along the=20
coast as far south as northwestern California more in deference to=20 uncertainty of timing as to the rainfall amounts.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7cIoHQfLo8NOX2dkS4Fwn7k_nYzWHFwlKyQblVmoK8is= J5jKbNHC7tQ1b2CBms4MfrS6qDEj0QDieThzrqy_XvPPvoc$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7cIoHQfLo8NOX2dkS4Fwn7k_nYzWHFwlKyQblVmoK8is= J5jKbNHC7tQ1b2CBms4MfrS6qDEj0QDieThzrqy_i7nMPDk$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7cIoHQfLo8NOX2dkS4Fwn7k_nYzWHFwlKyQblVmoK8is= J5jKbNHC7tQ1b2CBms4MfrS6qDEj0QDieThzrqy_xq5Jyfw$=20

=3D =3D =3D
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FOUS30 KWBC 140042
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
742 PM EST Sat Dec 13 2025

Day 1
Valid 01Z Sun Dec 14 2025 - 12Z Sun Dec 14 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
SOUTHEASTERN FLORIDA...

01Z Update...
HREF probs have come down with the 18Z run, but still show some=20
indication that showers and storms developing farther north along=20
the southeast coast of Florida may produce localized heavy amounts
along the urban corridor. Therefore, maintained the small Marginal
Risk.

Pereira

Previous discussion...
A weak mid-level wave over the eastern Gulf will aid in increasing
mid-level flow/ascent across the Florida Peninsula and adjacent
Gulf Stream during the overnight hours. Meanwhile, low-level
moisture will increase across coastal areas as a weak surface
boundary/inverted trough becomes established just inland across the
Peninsula. PW values should increase into the 1.6-1.8 inch range
amid 500+ J/kg SBCAPE. Meanwhile, point forecast soundings depict
favorable kinematic profiles for relatively slow-moving cells that
could impact urban areas of southeast Florida along the I-95
corridor. Local 1+ inch/hr rates are possible. Urban flash flooding
is possible in the 03-12Z timeframe this evening/tonight.

Cook

Day 2
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

..THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN WASHINGTON STATE LATE SUNDAY NIGHT/EARLY MONDAY MORNING...

2100 UTC Update -- No changes made to the Marginal Risk outlook
based on the new (12Z) guidance. 12Z HREF window runs through the
entire D2 period, and of note is the uptick in 0.50"/hr
probabilities after 06Z -- peaking over 80% across the Olympic
Ranges toward 12Z Mon, and over 40% across portions of the Cascades
in WA.

Hurley

Previous discussion...

Maintained the Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next push of moisture
approaches late Sunday night into the early morning hours of
Monday. The models have shown some run to run differences with QPF
but no real clear trend. One consistent signal is that the
orientation of the moisture plume remained more southwest-northeast
than the event that just ended a couple of days ago. That still
points to the idea that rainfall may not increase in coverage or
intensity until late in the Day 2 period. Based on the expected IVT
plume increasing to over 600 at about the time that the flow
reaches the coast and begins to take on more of an on- shore
component...am inclined to follow the ensemble idea of 0.75 inches
to locally 1.5 inches of precipitation focused in the terrain. The
area is sensitive given the nearly week-long excessive rainfall
event...so any additional rainfall is expected to bring renewed
hydrologic concerns. Given a fairly tight window of opportunity for
rainfall during the outlook period...and at least some questions
about timing of the onset....still think a Marginal Risk is
sufficient for now although later shifts can adjust if needed.

Bann

Day 3
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
WASHINGTON AND OREGON...

2100 UTC Update -- Only minor (cosmetic) changes made to the
previous D3 outlook, some of which was to pull the eastern edges of
the Slight ever so slightly westward in WA based on the latest
snowfall forecast (lowering snow levels).

Hurley

Previous discussion...

Areal coverage of rainfall expands and rain rates increase on
Monday as a well defined atmospheric river continues to direct
abundant moisture into the Washington coastal ranges and Cascades
that gradually makes its way southward into Oregon. Given
antecedent conditions from the excessive rainfall event from
earlier in the week plus whatever falls on Day 2...the concern is
for renewed flooding potential in addition to worsening on-going
flooding especially in the terrain with potential for additional
landslides or mudslides. Saw little reason to modify the Slight
risk area that propagated into the Day 3 period from yesterdays Day
4 outlook especially given the magnitude of the IVT and
precipitable water values forecast by the global models. The focus
of the heavy rainfall should gradually shift southward into an area
that did not receive as much rainfall from the previous
atmospheric river. Opted to extend a Marginal risk area along the
coast as far south as northwestern California more in deference to
uncertainty of timing as to the rainfall amounts.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7djc-qCKjvyN-vNjM1lH-JQP92RPyYeelgW1crOzG_Ch= 8W9W4QN7D6AobEeil4jOtWCDyUPUs8ffgJDgLzeajuTmtZw$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7djc-qCKjvyN-vNjM1lH-JQP92RPyYeelgW1crOzG_Ch= 8W9W4QN7D6AobEeil4jOtWCDyUPUs8ffgJDgLzeaypXRJGY$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7djc-qCKjvyN-vNjM1lH-JQP92RPyYeelgW1crOzG_Ch= 8W9W4QN7D6AobEeil4jOtWCDyUPUs8ffgJDgLzea4ceNwSo$=20

=3D =3D =3D
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FOUS30 KWBC 140821
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
321 AM EST Sun Dec 14 2025

Day 1
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A PORTION OF
WESTERN WASHINGTON...

Maintained the Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next real push of=20
moisture approaches later tonight into the early morning hours of=20
Monday. Any rainfall in Washington before then should be light and
on the periphery of a rain area directed on-shore north of the=20
international border. By 15/00Z...precipitable water values should
be approaching 1 inch along the coast as 850 mb winds approach the Washington/Oregon coast. Initially the 850 mb winds should have=20
more of a southerly than a westerly component...but eventually they
do take on a more orthogonal component to the Washington coast=20
ranges and Olympics. That is when the best chance for any excessive
rainfall is expected. Model guidance remains in the 0.5 to 0.75=20
inch range with locally 1.5 inches of precipitation focused in the=20
terrain. While these amounts are pretty modest for this part of the country...the area remains hydrologically sensitive given the=20
recent heavy to excessive rainfall event from earlier in the week=20
and even this amount of rainfall could result in renewed hydrologic concerns.=20

Bann

Day 2
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER WESTERN
WASHINGTON AND NORTHWEST OREGON...

Areal coverage of rainfall expands and rain rates increase on=20
Monday as a well defined atmospheric river continues to direct=20
abundant moisture into the Washington coastal ranges and Cascades.
IVT values approaching 800 is currently forecast along or near the
Washington coast as the Day 2 period begins...then weakens=20
somewhat as the axis progresses southward into Oregon. Given=20
antecedent conditions from the excessive rainfall event from=20
earlier in the week plus whatever falls on in the Day 1=20
period...the concern is for renewed flooding potential in addition=20
to worsening any on- going flooding. Given how water-logged the=20
soils have been...the potential is there for additional landslides=20
or mudslides. Saw little reason to modify the Slight risk area too=20 much...but continued the idea from yesterday in shrinking the=20
Slight risk area to minimize the overlap with heavy snow areas=20
(especially in the northern part of the Cascades as depicted by the
WPC Winter Weather desk). That being said...the overall forecast=20
reasoning changed little given the consistent magnitude of the=20 IVT/precipitable water values and QPF forecast by the global=20
models. The focus of the heavy rainfall should gradually shift=20
southward into an area that did not receive as much rainfall from=20
the previous atmospheric river.=20

Introduced a Marginal Risk area mainly focused over the Idaho
panhandle and a small portion of neighboring eastern Washington
mainly for later in the period. The Atmospheric River moisture
plume will be spreading increasing amounts of moisture into the
eastern part of Washington and northern Idaho. Deterministic QPF
approaching an inch is forecast for areas that had hydrologic
problems recently and concern is for additional problems.=20

Bann

Day 3
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL LINGERING OVER
PARTS OF THE PACIFIC NORTHWEST INTO FAR NORTHWEST CALIFORNIA...

Precipitation lingers from Washington southward along the Cascades
and the coastal ranges into northwest California on Tuesday and
into the early morning hours on Wednesday. With much of that
falling post-frontal and the heavier precipitation amounts falling
in the form of snow in the northern Cascades...will maintain the
Marginal Risk area for the time. Once again the main adjustments to
the outlook areas were to limit the overlap of excessive rainfall
with heavy areas mainly in Washington. The complex terrain of
northern Idaho and northwest MT made it difficult to avoid
overlapping but the idea is for any excessive rainfall to occur at
lower elevation locations in light of lowering thickness vales/snow levels.=20=20

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!67FMVwnM5PvBODTKoXt6tbq3YpsrpP4EDgqvdGgk26DD= Ol9SNODmDi-Afe8vOR-C5hTSnRwIqxM1R0oYQnJNGq-LOts$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!67FMVwnM5PvBODTKoXt6tbq3YpsrpP4EDgqvdGgk26DD= Ol9SNODmDi-Afe8vOR-C5hTSnRwIqxM1R0oYQnJNRIw89_I$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!67FMVwnM5PvBODTKoXt6tbq3YpsrpP4EDgqvdGgk26DD= Ol9SNODmDi-Afe8vOR-C5hTSnRwIqxM1R0oYQnJNbaexLBg$=20

=3D =3D =3D
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FOUS30 KWBC 141519
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1019 AM EST Sun Dec 14 2025

Day 1
Valid 16Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A PORTION OF
WESTERN WASHINGTON...

Maintained the Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next real push of
moisture approaches later tonight into the early morning hours of
Monday. Any rainfall in Washington before then should be light and
on the periphery of a rain area directed on-shore north of the
international border. By 15/00Z...precipitable water values should
be approaching 1 inch along the coast as 850 mb winds approach the Washington/Oregon coast. Initially the 850 mb winds should have
more of a southerly than a westerly component...but eventually they
do take on a more orthogonal component to the Washington coast
ranges and Olympics. That is when the best chance for any excessive
rainfall is expected. Model guidance remains in the 0.5 to 0.75
inch range with locally 1.5 inches of precipitation focused in the
terrain. While these amounts are pretty modest for this part of the country...the area remains hydrologically sensitive given the
recent heavy to excessive rainfall event from earlier in the week
and even this amount of rainfall could result in renewed hydrologic
concerns.

Cook/Bann

Day 2
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER WESTERN
WASHINGTON AND NORTHWEST OREGON...

Areal coverage of rainfall expands and rain rates increase on
Monday as a well defined atmospheric river continues to direct
abundant moisture into the Washington coastal ranges and Cascades.
IVT values approaching 800 is currently forecast along or near the
Washington coast as the Day 2 period begins...then weakens
somewhat as the axis progresses southward into Oregon. Given
antecedent conditions from the excessive rainfall event from
earlier in the week plus whatever falls on in the Day 1
period...the concern is for renewed flooding potential in addition
to worsening any on- going flooding. Given how water-logged the
soils have been...the potential is there for additional landslides
or mudslides. Saw little reason to modify the Slight risk area too
much...but continued the idea from yesterday in shrinking the
Slight risk area to minimize the overlap with heavy snow areas
(especially in the northern part of the Cascades as depicted by the
WPC Winter Weather desk). That being said...the overall forecast
reasoning changed little given the consistent magnitude of the
IVT/precipitable water values and QPF forecast by the global
models. The focus of the heavy rainfall should gradually shift
southward into an area that did not receive as much rainfall from
the previous atmospheric river.

Introduced a Marginal Risk area mainly focused over the Idaho
panhandle and a small portion of neighboring eastern Washington
mainly for later in the period. The Atmospheric River moisture
plume will be spreading increasing amounts of moisture into the
eastern part of Washington and northern Idaho. Deterministic QPF
approaching an inch is forecast for areas that had hydrologic
problems recently and concern is for additional problems.

Bann

Day 3
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL LINGERING OVER
PARTS OF THE PACIFIC NORTHWEST INTO FAR NORTHWEST CALIFORNIA...

Precipitation lingers from Washington southward along the Cascades
and the coastal ranges into northwest California on Tuesday and
into the early morning hours on Wednesday. With much of that
falling post-frontal and the heavier precipitation amounts falling
in the form of snow in the northern Cascades...will maintain the
Marginal Risk area for the time. Once again the main adjustments to
the outlook areas were to limit the overlap of excessive rainfall
with heavy areas mainly in Washington. The complex terrain of
northern Idaho and northwest MT made it difficult to avoid
overlapping but the idea is for any excessive rainfall to occur at
lower elevation locations in light of lowering thickness vales/snow
levels.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8zU6hpjft11jNctHuToqxms-ZUzde2dEF74X5C42eyFo= RuwQgUxRIkvHn-osLcJqJIZBAHcAVql7mhYOhRriO0rXlp0$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8zU6hpjft11jNctHuToqxms-ZUzde2dEF74X5C42eyFo= RuwQgUxRIkvHn-osLcJqJIZBAHcAVql7mhYOhRrix01dugM$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8zU6hpjft11jNctHuToqxms-ZUzde2dEF74X5C42eyFo= RuwQgUxRIkvHn-osLcJqJIZBAHcAVql7mhYOhRrisq3HAdw$=20

=3D =3D =3D
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FOUS30 KWBC 141941
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
241 PM EST Sun Dec 14 2025

Day 1
Valid 16Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A PORTION OF
WESTERN WASHINGTON...

Maintained the Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next real push of
moisture approaches later tonight into the early morning hours of
Monday. Any rainfall in Washington before then should be light and
on the periphery of a rain area directed on-shore north of the
international border. By 15/00Z...precipitable water values should
be approaching 1 inch along the coast as 850 mb winds approach the Washington/Oregon coast. Initially the 850 mb winds should have
more of a southerly than a westerly component...but eventually they
do take on a more orthogonal component to the Washington coast
ranges and Olympics. That is when the best chance for any excessive
rainfall is expected. Model guidance remains in the 0.5 to 0.75
inch range with locally 1.5 inches of precipitation focused in the
terrain. While these amounts are pretty modest for this part of the country...the area remains hydrologically sensitive given the
recent heavy to excessive rainfall event from earlier in the week
and even this amount of rainfall could result in renewed hydrologic
concerns.

Cook/Bann

Day 2
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER WESTERN
WASHINGTON AND NORTHWEST OREGON...

...2000 UTC Update...
Trimmed a little bit of the Slight Risk area on the western slopes
of the Cascades (above 3500 ft) due to the lowering snow levels=20
with time during the period. Otherwise, also made minor adjustments
to the Marginal Risk area over northeast WA-northern ID-northwest
MT, based on the new (12Z) guidance QPFs and HREF exceedance
probabilities.

Hurley

...Previous discussion...
Areal coverage of rainfall expands and rain rates increase on=20
Monday as a well defined atmospheric river continues to direct=20
abundant moisture into the Washington coastal ranges and Cascades.=20
IVT values approaching 800 is currently forecast along or near the=20 Washington coast as the Day 2 period begins...then weakens somewhat
as the axis progresses southward into Oregon. Given antecedent=20
conditions from the excessive rainfall event from earlier in the=20
week plus whatever falls on in the Day 1 period...the concern is=20
for renewed flooding potential in addition to worsening any on-=20
going flooding. Given how water-logged the soils have been...the=20
potential is there for additional landslides or mudslides. Saw=20
little reason to modify the Slight risk area too much...but=20
continued the idea from yesterday in shrinking the Slight risk area
to minimize the overlap with heavy snow areas (especially in the=20
northern part of the Cascades as depicted by the WPC Winter Weather
desk). That being said...the overall forecast reasoning changed=20
little given the consistent magnitude of the IVT/precipitable water
values and QPF forecast by the global models. The focus of the=20
heavy rainfall should gradually shift southward into an area that=20
did not receive as much rainfall from the previous atmospheric=20
river.

Introduced a Marginal Risk area mainly focused over the Idaho
panhandle and a small portion of neighboring eastern Washington
mainly for later in the period. The Atmospheric River moisture
plume will be spreading increasing amounts of moisture into the
eastern part of Washington and northern Idaho. Deterministic QPF
approaching an inch is forecast for areas that had hydrologic
problems recently and concern is for additional problems.

Bann

Day 3
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL LINGERING OVER
PARTS OF THE PACIFIC NORTHWEST INTO FAR NORTHWEST CALIFORNIA...

...2000 UTC Update...
Based on the latest (12Z) model QPFs and trends (lower ensemble=20
means), along with the lowering snow levels, have removed the=20
Marginal Risk area that was in play across northern ID into
northwest MT). QPFs across the Sierra meanwhile average between
0.5-1.0" during the 24 hr period; given this along with the absence
of any elevated instability, have removed the Marginal area that
was in effect over the northern Sierra.=20

Hurley

...Previous Discussion...
Precipitation lingers from Washington southward along the Cascades
and the coastal ranges into northwest California on Tuesday and=20
into the early morning hours on Wednesday. With much of that=20
falling post-frontal and the heavier precipitation amounts falling=20
in the form of snow in the northern Cascades...will maintain the=20
Marginal Risk area for the time. Once again the main adjustments to
the outlook areas were to limit the overlap of excessive rainfall=20
with heavy areas mainly in Washington.=20

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5yNkxCb8_S9oSxzEgKFF_kaPOuaQpTkqelgWNjRux00H= I4trA3hRUQejMzBLt2TLBMb0F_UoK6zKNyueAVb5PaMqkXU$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5yNkxCb8_S9oSxzEgKFF_kaPOuaQpTkqelgWNjRux00H= I4trA3hRUQejMzBLt2TLBMb0F_UoK6zKNyueAVb5KaM9wlw$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5yNkxCb8_S9oSxzEgKFF_kaPOuaQpTkqelgWNjRux00H= I4trA3hRUQejMzBLt2TLBMb0F_UoK6zKNyueAVb5U5Ko5jA$=20

=3D =3D =3D
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FOUS30 KWBC 150035
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
735 PM EST Sun Dec 14 2025

Day 1
Valid 01Z Mon Dec 15 2025 - 12Z Mon Dec 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A PORTION OF
WESTERN WASHINGTON...

01Z Update...
No changes to the previous outlook.

Pereira

Previous discussion...
Maintained the Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next real push of
moisture approaches later tonight into the early morning hours of
Monday. Any rainfall in Washington before then should be light and
on the periphery of a rain area directed on-shore north of the
international border. By 15/00Z...precipitable water values should
be approaching 1 inch along the coast as 850 mb winds approach the Washington/Oregon coast. Initially the 850 mb winds should have
more of a southerly than a westerly component...but eventually they
do take on a more orthogonal component to the Washington coast
ranges and Olympics. That is when the best chance for any excessive
rainfall is expected. Model guidance remains in the 0.5 to 0.75
inch range with locally 1.5 inches of precipitation focused in the
terrain. While these amounts are pretty modest for this part of the country...the area remains hydrologically sensitive given the
recent heavy to excessive rainfall event from earlier in the week
and even this amount of rainfall could result in renewed hydrologic
concerns.

Cook/Bann

Day 2
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER WESTERN
WASHINGTON AND NORTHWEST OREGON...

...2000 UTC Update...
Trimmed a little bit of the Slight Risk area on the western slopes
of the Cascades (above 3500 ft) due to the lowering snow levels
with time during the period. Otherwise, also made minor adjustments
to the Marginal Risk area over northeast WA-northern ID-northwest
MT, based on the new (12Z) guidance QPFs and HREF exceedance
probabilities.

Hurley

...Previous discussion...
Areal coverage of rainfall expands and rain rates increase on
Monday as a well defined atmospheric river continues to direct
abundant moisture into the Washington coastal ranges and Cascades.
IVT values approaching 800 is currently forecast along or near the
Washington coast as the Day 2 period begins...then weakens somewhat
as the axis progresses southward into Oregon. Given antecedent
conditions from the excessive rainfall event from earlier in the
week plus whatever falls on in the Day 1 period...the concern is
for renewed flooding potential in addition to worsening any on-
going flooding. Given how water-logged the soils have been...the
potential is there for additional landslides or mudslides. Saw
little reason to modify the Slight risk area too much...but
continued the idea from yesterday in shrinking the Slight risk area
to minimize the overlap with heavy snow areas (especially in the
northern part of the Cascades as depicted by the WPC Winter Weather
desk). That being said...the overall forecast reasoning changed
little given the consistent magnitude of the IVT/precipitable water
values and QPF forecast by the global models. The focus of the
heavy rainfall should gradually shift southward into an area that
did not receive as much rainfall from the previous atmospheric
river.

Introduced a Marginal Risk area mainly focused over the Idaho
panhandle and a small portion of neighboring eastern Washington
mainly for later in the period. The Atmospheric River moisture
plume will be spreading increasing amounts of moisture into the
eastern part of Washington and northern Idaho. Deterministic QPF
approaching an inch is forecast for areas that had hydrologic
problems recently and concern is for additional problems.

Bann

Day 3
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL LINGERING OVER
PARTS OF THE PACIFIC NORTHWEST INTO FAR NORTHWEST CALIFORNIA...

...2000 UTC Update...
Based on the latest (12Z) model QPFs and trends (lower ensemble
means), along with the lowering snow levels, have removed the
Marginal Risk area that was in play across northern ID into
northwest MT). QPFs across the Sierra meanwhile average between
0.5-1.0" during the 24 hr period; given this along with the absence
of any elevated instability, have removed the Marginal area that
was in effect over the northern Sierra.

Hurley

...Previous Discussion...
Precipitation lingers from Washington southward along the Cascades
and the coastal ranges into northwest California on Tuesday and
into the early morning hours on Wednesday. With much of that
falling post-frontal and the heavier precipitation amounts falling
in the form of snow in the northern Cascades...will maintain the
Marginal Risk area for the time. Once again the main adjustments to
the outlook areas were to limit the overlap of excessive rainfall
with heavy areas mainly in Washington.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_GwMfYI01ZApjQ6lUw_26GUTnkjjjaMtAjTaM_EctNoF= PhqQEwb58BBhnsp_cyElnww0DwuMPnjguSGDclpUfzPsdBM$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_GwMfYI01ZApjQ6lUw_26GUTnkjjjaMtAjTaM_EctNoF= PhqQEwb58BBhnsp_cyElnww0DwuMPnjguSGDclpUBiqCpV4$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_GwMfYI01ZApjQ6lUw_26GUTnkjjjaMtAjTaM_EctNoF= PhqQEwb58BBhnsp_cyElnww0DwuMPnjguSGDclpUpiVrS6g$=20

=3D =3D =3D
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FOUS30 KWBC 150832
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
332 AM EST Mon Dec 15 2025

Day 1
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WASHINGTON AND OREGON TODAY AND TONIGHT...

Overall...the changes were fairly minor as yesterday's Day 2=20
Excessive Rainfall Outlook propagated into today's Day 1 outlook.=20
There were a few run to run differences in the deterministic and=20 probabilistic runs...especially over northeast Washington- northern
Idaho and northwest Montana. The broad forecast reasoning did not=20 fundamentally shift.=20

The areal coverage of rainfall expands and rain rates increase
early today as a well defined atmospheric river continues to=20
direct abundant moisture into the Washington coastal ranges and=20
Cascades. IVT values in excess of 700 kg per meter per second early
today will be spreading inland but weaken as the axis makes its way
inland and as the axis of best moisture transport gets directed
southward into Oregon. Given antecedent conditions...the forecast
of another 3 or 4 inches in the terrain raises concerns of worsening
any on-going flooding and result in new areas. In
addition...considering how water-logged the soils became in the
recent heavy to excessive rainfall event...the potential is there=20
for additional landslides or mudslides. Latest guidance still
showed the nose of the moisture plume getting as far east as parts
of eastern Washington....northern Idaho and northwest Montana where
a second and more focused Marginal Risk area remained. The focus=20
of the heavy rainfall should gradually shift southward into an area
that did not receive as much rainfall from the previous atmospheric
river and has had a chance to drain off some of that water.=20=20

Bann

Day 2
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PACIFIC NORTHWEST...

Maintained the previously issued Marginal Risk area from=20
Washington southward along the Cascades and the coastal ranges into
northwest California on Tuesday and early Wednesday. Latest=20
deterministic and ensemble guidance showed the highest QPF in the=20
complex terrain...rivaling the QPF on Day 1 in some places in=20
Washington. The main reason for holding with a Marginal Risk area=20
was due to the lowering snow-levels given post-frontal lowering of=20 heights/thickness values that result in snow. Even so...did expand=20
the eastern boundary of the Marginal Risk area a bit to the east in
Washington and a portion of nearby Oregon. While this resulted in=20
some additional overlap with snow areas...the idea was to capture=20
some of the higher QPF amounts from regions where (presumably) the=20 precipitation started as rain and then transitioned to snow. Tried=20
to avoid overlap with the Winter Weather Desk snow amounts of 6=20
inches or greater.=20

The overall synoptic pattern continued to show the deepest moisture
and broadest coverage of rainfall arriving in association with the
surface cold front around 17/00Z and the diminishing QPF as the
area gets whisked eastward.

Bann

Day 3
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

...THE MARGINAL RISK OF EXCESSIVE RAINFALL AREA LINGERS OVER PARTS
OF THE PACIFIC NORTHWEST. ON WEDNESDAY...

There should be a relative lull in activity across parts of
Washington...Oregon and northern California in the wake of a system
on Tuesday into early Wednesday. Even though there may still be
some rainfall that lingers into Day 3...the Marginal Risk area was
maintained in deference to the approach of the next and seemingly
stronger AR on Day 4 and to account for the possibility that the=20
guidance could be too slow with the onset of rainfall with this
system. Refer to guidance from the WPC Medium Range Desk for
additional info. Even if the rainfall associated with the next
system does not arrive prior to 12Z Thursday as shown by the
models...any lingering rainfall still has the potential for be
impactful in the most hydrologically sensitive areas.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5EjH_1ZQ6D4ZDlLOoXLMyMgTdOjxIkqnF7_YFDK5M9TZ= 825cFnHr32W5bL_XuxNbiCHyt3aHmrRJbPd6I8b_dJcEJ6Q$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5EjH_1ZQ6D4ZDlLOoXLMyMgTdOjxIkqnF7_YFDK5M9TZ= 825cFnHr32W5bL_XuxNbiCHyt3aHmrRJbPd6I8b_FUXIHa0$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5EjH_1ZQ6D4ZDlLOoXLMyMgTdOjxIkqnF7_YFDK5M9TZ= 825cFnHr32W5bL_XuxNbiCHyt3aHmrRJbPd6I8b_IPAtlc0$=20

=3D =3D =3D
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FOUS30 KWBC 151559
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1059 AM EST Mon Dec 15 2025

Day 1
Valid 16Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WASHINGTON AND OREGON TODAY AND TONIGHT...

...16Z update...

IVT values approaching 1000 kg/m/s were found offshore and to the
coastline of southern Washington/northern Oregon between 12-15Z=20
this morning with 60-70 kt of flow in the 850-700 mb layer. Peak=20
3-hr rainfall of 1.0 to 1.3 inches was observed for the Olympics=20
and isolated spots within the northern Washington Cascades ending
15Z. IVT values will drop off across western Washington/Oregon=20
through the day today as the moisture axis pushes east and south,
out ahead of a cold front. Snow levels will also fall behind the
cold front to about 6000 ft by 00Z and lower to near 3000 ft for
the northern Cascades by 12Z Tuesday.=20

The Slight Risk was maintained given the wet antecedent conditions
and ongoing rainfall. The potential will exist for an additional 2
to 3 inches of rain through 12Z (maximum values), although rain
rates will be much lower than this morning with occasional 0.25+
in/hr rates and perhaps an isolated spot with 0.5 in/hr where weak
instability combines with strong left-exit jet stream forcing and
continued onshore flow.

Elsewhere, the forecast remains on track with a surge of heavier
rainfall likely to impact portions of the northern Rockies over the
next 3-6 hours followed by locally high rain rates in excess of
0.5 in/hr for the coast of Oregon into northern California where=20
the Marginal Risk was maintained.

Otto

...previous discussion follows...


Overall...the changes were fairly minor as yesterday's Day 2
Excessive Rainfall Outlook propagated into today's Day 1 outlook.
There were a few run to run differences in the deterministic and
probabilistic runs...especially over northeast Washington- northern
Idaho and northwest Montana. The broad forecast reasoning did not
fundamentally shift.

The areal coverage of rainfall expands and rain rates increase
early today as a well defined atmospheric river continues to
direct abundant moisture into the Washington coastal ranges and
Cascades. IVT values in excess of 700 kg per meter per second early
today will be spreading inland but weaken as the axis makes its way
inland and as the axis of best moisture transport gets directed
southward into Oregon. Given antecedent conditions...the forecast
of another 3 or 4 inches in the terrain raises concerns of worsening
any on-going flooding and result in new areas. In
addition...considering how water-logged the soils became in the
recent heavy to excessive rainfall event...the potential is there
for additional landslides or mudslides. Latest guidance still
showed the nose of the moisture plume getting as far east as parts
of eastern Washington....northern Idaho and northwest Montana where
a second and more focused Marginal Risk area remained. The focus
of the heavy rainfall should gradually shift southward into an area
that did not receive as much rainfall from the previous atmospheric
river and has had a chance to drain off some of that water.

Bann

Day 2
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PACIFIC NORTHWEST...

Maintained the previously issued Marginal Risk area from
Washington southward along the Cascades and the coastal ranges into
northwest California on Tuesday and early Wednesday. Latest
deterministic and ensemble guidance showed the highest QPF in the
complex terrain...rivaling the QPF on Day 1 in some places in
Washington. The main reason for holding with a Marginal Risk area
was due to the lowering snow-levels given post-frontal lowering of heights/thickness values that result in snow. Even so...did expand
the eastern boundary of the Marginal Risk area a bit to the east in
Washington and a portion of nearby Oregon. While this resulted in
some additional overlap with snow areas...the idea was to capture
some of the higher QPF amounts from regions where (presumably) the precipitation started as rain and then transitioned to snow. Tried
to avoid overlap with the Winter Weather Desk snow amounts of 6
inches or greater.

The overall synoptic pattern continued to show the deepest moisture
and broadest coverage of rainfall arriving in association with the
surface cold front around 17/00Z and the diminishing QPF as the
area gets whisked eastward.

Bann

Day 3
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

...THE MARGINAL RISK OF EXCESSIVE RAINFALL AREA LINGERS OVER PARTS
OF THE PACIFIC NORTHWEST. ON WEDNESDAY...

There should be a relative lull in activity across parts of
Washington...Oregon and northern California in the wake of a system
on Tuesday into early Wednesday. Even though there may still be
some rainfall that lingers into Day 3...the Marginal Risk area was
maintained in deference to the approach of the next and seemingly
stronger AR on Day 4 and to account for the possibility that the
guidance could be too slow with the onset of rainfall with this
system. Refer to guidance from the WPC Medium Range Desk for
additional info. Even if the rainfall associated with the next
system does not arrive prior to 12Z Thursday as shown by the
models...any lingering rainfall still has the potential for be
impactful in the most hydrologically sensitive areas.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6Dos-5Xa0AOC399QnaDeDG-yTPil_A4m5e0sWysxwqcu= dibtTBj6C1xRKxBsZYZR7nlAwCYeHqs1S-yIBjnc_O0JQB8$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6Dos-5Xa0AOC399QnaDeDG-yTPil_A4m5e0sWysxwqcu= dibtTBj6C1xRKxBsZYZR7nlAwCYeHqs1S-yIBjncTwnF_rg$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6Dos-5Xa0AOC399QnaDeDG-yTPil_A4m5e0sWysxwqcu= dibtTBj6C1xRKxBsZYZR7nlAwCYeHqs1S-yIBjncqejO9Lw$=20

=3D =3D =3D
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FOUS30 KWBC 152016
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
316 PM EST Mon Dec 15 2025

Day 1
Valid 16Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WASHINGTON AND OREGON TODAY AND TONIGHT...

...16Z update...

IVT values approaching 1000 kg/m/s were found offshore and to the
coastline of southern Washington/northern Oregon between 12-15Z
this morning with 60-70 kt of flow in the 850-700 mb layer. Peak
3-hr rainfall of 1.0 to 1.3 inches was observed for the Olympics
and isolated spots within the northern Washington Cascades ending
15Z. IVT values will drop off across western Washington/Oregon
through the day today as the moisture axis pushes east and south,
out ahead of a cold front. Snow levels will also fall behind the
cold front to about 6000 ft by 00Z and lower to near 3000 ft for
the northern Cascades by 12Z Tuesday.

The Slight Risk was maintained given the wet antecedent conditions
and ongoing rainfall. The potential will exist for an additional 2
to 3 inches of rain through 12Z (maximum values), although rain
rates will be much lower than this morning with occasional 0.25+
in/hr rates and perhaps an isolated spot with 0.5 in/hr where weak
instability combines with strong left-exit jet stream forcing and
continued onshore flow.

Elsewhere, the forecast remains on track with a surge of heavier
rainfall likely to impact portions of the northern Rockies over the
next 3-6 hours followed by locally high rain rates in excess of
0.5 in/hr for the coast of Oregon into northern California where
the Marginal Risk was maintained.

Otto

...previous discussion follows...


Overall...the changes were fairly minor as yesterday's Day 2
Excessive Rainfall Outlook propagated into today's Day 1 outlook.
There were a few run to run differences in the deterministic and
probabilistic runs...especially over northeast Washington- northern
Idaho and northwest Montana. The broad forecast reasoning did not
fundamentally shift.

The areal coverage of rainfall expands and rain rates increase
early today as a well defined atmospheric river continues to
direct abundant moisture into the Washington coastal ranges and
Cascades. IVT values in excess of 700 kg per meter per second early
today will be spreading inland but weaken as the axis makes its way
inland and as the axis of best moisture transport gets directed
southward into Oregon. Given antecedent conditions...the forecast
of another 3 or 4 inches in the terrain raises concerns of worsening
any on-going flooding and result in new areas. In
addition...considering how water-logged the soils became in the
recent heavy to excessive rainfall event...the potential is there
for additional landslides or mudslides. Latest guidance still
showed the nose of the moisture plume getting as far east as parts
of eastern Washington....northern Idaho and northwest Montana where
a second and more focused Marginal Risk area remained. The focus
of the heavy rainfall should gradually shift southward into an area
that did not receive as much rainfall from the previous=20
atmospheric river and has had a chance to drain off some of that=20
water.

Bann

Day 2
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PACIFIC NORTHWEST...

Maintained the previously issued Marginal Risk area from
Washington southward along the Cascades and the coastal ranges into
northwest California on Tuesday and early Wednesday. Latest
deterministic and ensemble guidance showed the highest QPF in the
complex terrain...rivaling the QPF on Day 1 in some places in
Washington. The main reason for holding with a Marginal Risk area
was due to the lowering snow-levels given post-frontal lowering of heights/thickness values that result in snow. Even so...did expand
the eastern boundary of the Marginal Risk area a bit to the east in
Washington and a portion of nearby Oregon. While this resulted in
some additional overlap with snow areas...the idea was to capture
some of the higher QPF amounts from regions where (presumably) the precipitation started as rain and then transitioned to snow. Tried
to avoid overlap with the Winter Weather Desk snow amounts of 6
inches or greater.

The overall synoptic pattern continued to show the deepest moisture
and broadest coverage of rainfall arriving in association with the
surface cold front around 17/00Z and the diminishing QPF as the
area gets whisked eastward.

Cook/Bann

Day 3
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

...THE MARGINAL RISK OF EXCESSIVE RAINFALL AREA LINGERS OVER PARTS
OF THE PACIFIC NORTHWEST. ON WEDNESDAY...

There should be a relative lull in activity across parts of
Washington...Oregon and northern California in the wake of a system
on Tuesday into early Wednesday. Even though there may still be
some rainfall that lingers into Day 3...the Marginal Risk area was
maintained in deference to the approach of the next and seemingly
stronger AR on Day 4 and to account for the possibility that the
guidance could be too slow with the onset of rainfall with this
system. Refer to guidance from the WPC Medium Range Desk for
additional info. Even if the rainfall associated with the next
system does not arrive prior to 12Z Thursday as shown by the
models...any lingering rainfall still has the potential for be
impactful in the most hydrologically sensitive areas.

Cook/Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!41TtQ_L5IEVVj3LCzu9o5i1FvXVLhZiCRv-i15hU1NRB= fnSkYcArsrIeQm1axtdO5Jkku8zkOeB6IYpu9uUY916pxF0$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!41TtQ_L5IEVVj3LCzu9o5i1FvXVLhZiCRv-i15hU1NRB= fnSkYcArsrIeQm1axtdO5Jkku8zkOeB6IYpu9uUY5AT1nGw$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!41TtQ_L5IEVVj3LCzu9o5i1FvXVLhZiCRv-i15hU1NRB= fnSkYcArsrIeQm1axtdO5Jkku8zkOeB6IYpu9uUYYhOufH0$=20

=3D =3D =3D
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FOUS30 KWBC 160031
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
731 PM EST Mon Dec 15 2025

Day 1
Valid 01Z Tue Dec 16 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WASHINGTON AND OREGON TODAY AND TONIGHT...

While IVT values continue to drop off across western=20
Washington/Oregon as the moisture axis pushes east and south, a
renewed surge of heavy rainfall is possible around the coast of WA
at the end of the period early Tuesday morning. Snow levels will=20
lower to near 3000 ft for the northern Cascades by 12Z Tuesday.

The Slight Risk was maintained given the wet antecedent conditions
and ongoing rainfall. The potential will exist for an additional 1
to 2 inches of rain through 12Z (maximum values), with hourly rain
amounts maximizing in the 0.25-0.50" range where weak instability=20
combines with strong left- exit jet stream forcing and continued=20
onshore flow. The main adjustment to the ERO areas was to remove
portions of their southern areas in OR where the 18z HREF no=20
longer supports heavy rains.

A surge of heavier rainfall impacting portions of the northern=20
Rockies early on with hourly rain amounts of 0.5"+ should weaken
overnight.=20

Roth


Day 2
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PACIFIC NORTHWEST...

Maintained the previously issued Marginal Risk area from
Washington southward along the Cascades and the coastal ranges into
northwest California on Tuesday and early Wednesday. Latest
deterministic and ensemble guidance showed the highest QPF in the
complex terrain...rivaling the QPF on Day 1 in some places in
Washington. The main reason for holding with a Marginal Risk area
was due to the lowering snow-levels given post-frontal lowering of heights/thickness values that result in snow. Even so...did expand
the eastern boundary of the Marginal Risk area a bit to the east in
Washington and a portion of nearby Oregon. While this resulted in
some additional overlap with snow areas...the idea was to capture
some of the higher QPF amounts from regions where (presumably) the precipitation started as rain and then transitioned to snow. Tried
to avoid overlap with the Winter Weather Desk snow amounts of 6
inches or greater.

The overall synoptic pattern continued to show the deepest moisture
and broadest coverage of rainfall arriving in association with the
surface cold front around 17/00Z and the diminishing QPF as the
area gets whisked eastward.

Cook/Bann

Day 3
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

...THE MARGINAL RISK OF EXCESSIVE RAINFALL AREA LINGERS OVER PARTS
OF THE PACIFIC NORTHWEST. ON WEDNESDAY...

There should be a relative lull in activity across parts of
Washington...Oregon and northern California in the wake of a system
on Tuesday into early Wednesday. Even though there may still be
some rainfall that lingers into Day 3...the Marginal Risk area was
maintained in deference to the approach of the next and seemingly
stronger AR on Day 4 and to account for the possibility that the
guidance could be too slow with the onset of rainfall with this
system. Refer to guidance from the WPC Medium Range Desk for
additional info. Even if the rainfall associated with the next
system does not arrive prior to 12Z Thursday as shown by the
models...any lingering rainfall still has the potential for be
impactful in the most hydrologically sensitive areas.

Cook/Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-otCM6UTTMIpZelTUFFMs4gE4dTzxJyZzFgGZ6glWCWF= BO9yAHV9ZZW-Y-oLbsaSKq8Vk9dxdoZsjDZAgqIBZ2oktpU$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-otCM6UTTMIpZelTUFFMs4gE4dTzxJyZzFgGZ6glWCWF= BO9yAHV9ZZW-Y-oLbsaSKq8Vk9dxdoZsjDZAgqIBeSvYnis$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-otCM6UTTMIpZelTUFFMs4gE4dTzxJyZzFgGZ6glWCWF= BO9yAHV9ZZW-Y-oLbsaSKq8Vk9dxdoZsjDZAgqIBstkXtjM$=20

=3D =3D =3D
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FOUS30 KWBC 160825
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
325 AM EST Tue Dec 16 2025

Day 1
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PACIFIC NORTHWEST...

Maintained the previously issued Marginal Risk area from
Washington southward along the Cascades and the coastal ranges into
northwest California today and tonight. Yet another round of
precipitation will be spreading from west to east across portions
of Washington and Oregon. Cooler air coming in behind the system
should result in mountain snows and rain for the lowlands and
mountain passes today into tonight. There should be a separate area
of mainly rain and some higher level snows that gets directed into
the southwest portion and northwest corner of California with
amounts locally enhanced by orographic influences. The previous
outlook largely covered this scenario so few changes were
needed.Once again...some overlap between the excessive rainfall
areas and mountain snowfall amounts was unavoidable but we tried=20
to keep the ERO away from the placement of the WPC Winter Weather=20
Desk snow amounts of 6 inches or greater.

The overall synoptic pattern continued to show the deepest moisture
and broadest coverage of rainfall arriving in association with the
surface cold front around 17/00Z and the diminishing QPF as the
area gets whisked eastward.

Bann

Day 2
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

QPF from the 16/00Z operational and ensemble guidance continued to
trend down with a correspondingly smaller risk of excessive=20
rainfall. That...combined with the higher precipitation amounts
being confined to higher elevations in Washington where
precipitation type would mainly be snow...should limit the overall risk
of excessive rainfall to less than 5 percent.=20

Bann

Day 3
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER MUCH OF
WESTERN OREGON AND PORTIONS OF ADJOINING STATES...

The next in a series of Atmospheric Rivers will arrive early
Thursday with its axis of greatest moisture transport being=20
directed primarily along the western coast of Oregon...with maximum
IVT values in excess of 800 kg per meter per second largely being=20
directed perpendicular into the coastal ranges early in the period.
Global models continue to advertise the possibility of 6 inches or
more of rainfall during the period...and comparing the WPC 24hr=20
QPF to ARI yielded a broad swath exceeding the 2-5 year return=20
intervals. It was also worth noting that the highest ARIs were just
to the east of the crest of the Cascades where an axis of 25-100=20
year exceedance intervals was depicted. This does seem like a=20
scenario where more spillover into the normally drier downslope=20
areas is plausible, so could be an impactful event even into some=20
of those areas. Consequently, the Day 3 excessive rainfall outlook=20
expanded the Slight Risk eastward in Oregon to cover areas with QPF
in excess of 5 inches and the highest ARI values mentioned above=20
given the concern for spillover. Snowfall within this area should=20
be confined to the higher elevations.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_pZ_t1KkTQLfFl-j-fVeLC_mq4IrNfgKzBTLuWHcU6Wc= 98EgRjF5fcHAfu1nmIOWQm-88rdLTUljSXMX3u3pJyE8EEM$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_pZ_t1KkTQLfFl-j-fVeLC_mq4IrNfgKzBTLuWHcU6Wc= 98EgRjF5fcHAfu1nmIOWQm-88rdLTUljSXMX3u3pSCytKOk$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_pZ_t1KkTQLfFl-j-fVeLC_mq4IrNfgKzBTLuWHcU6Wc= 98EgRjF5fcHAfu1nmIOWQm-88rdLTUljSXMX3u3p4xw8Qf4$=20

=3D =3D =3D
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FOUS30 KWBC 161541
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1041 AM EST Tue Dec 16 2025

Day 1
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PACIFIC NORTHWEST...

16z update:
The timing/placement of the quick hitting A.R. surge remains on
track with reinvigoration of the NW California portion will
generally start around 20-21z before expanding northward with the
core of the northern stream southwesterly deep jet streak reaching
NW Oregon just before 06z. IVT values are well above normal due to
the strength of deep layer flow, peaking near 900 kg/m/s. The
duration of the core of the AR surge will likely be ending about
12z-15z. Additional 1-2" for the lower coastal ranges are expected
with spots of 2-3" in the mid-slopes of the Cascade, Olympic ranges
with only a few highest peaks near the Klamath Range near 4" by
12z. As such, no changes were made to the broad Marginal Risk of
Excessive Rainfall.=20

Gallina

~~~~Prior Discussion~~~~
Maintained the previously issued Marginal Risk area from=20
Washington southward along the Cascades and the coastal ranges into
northwest California today and tonight. Yet another round of=20
precipitation will be spreading from west to east across portions=20
of Washington and Oregon. Cooler air coming in behind the system=20
should result in mountain snows and rain for the lowlands and=20
mountain passes today into tonight. There should be a separate area
of mainly rain and some higher level snows that gets directed into
the southwest portion and northwest corner of California with=20
amounts locally enhanced by orographic influences. The previous=20
outlook largely covered this scenario so few changes were=20
needed.Once again...some overlap between the excessive rainfall=20
areas and mountain snowfall amounts was unavoidable but we tried to
keep the ERO away from the placement of the WPC Winter Weather=20
Desk snow amounts of 6 inches or greater.

The overall synoptic pattern continued to show the deepest moisture
and broadest coverage of rainfall arriving in association with the
surface cold front around 17/00Z and the diminishing QPF as the
area gets whisked eastward.

Bann

Day 2
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

QPF from the 16/00Z operational and ensemble guidance continued to
trend down with a correspondingly smaller risk of excessive
rainfall. That...combined with the higher precipitation amounts
being confined to higher elevations in Washington where
precipitation type would mainly be snow...should limit the overall risk
of excessive rainfall to less than 5 percent.

Bann

Day 3
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER MUCH OF
WESTERN OREGON AND PORTIONS OF ADJOINING STATES...

The next in a series of Atmospheric Rivers will arrive early
Thursday with its axis of greatest moisture transport being
directed primarily along the western coast of Oregon...with maximum
IVT values in excess of 800 kg per meter per second largely being
directed perpendicular into the coastal ranges early in the period.
Global models continue to advertise the possibility of 6 inches or
more of rainfall during the period...and comparing the WPC 24hr
QPF to ARI yielded a broad swath exceeding the 2-5 year return
intervals. It was also worth noting that the highest ARIs were just
to the east of the crest of the Cascades where an axis of 25-100
year exceedance intervals was depicted. This does seem like a
scenario where more spillover into the normally drier downslope
areas is plausible, so could be an impactful event even into some
of those areas. Consequently, the Day 3 excessive rainfall outlook
expanded the Slight Risk eastward in Oregon to cover areas with QPF
in excess of 5 inches and the highest ARI values mentioned above
given the concern for spillover. Snowfall within this area should
be confined to the higher elevations.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8SqJ5i9DYfttxr9F6YvXfVyCrV5cDroE-n5TCcr0qAvt= dGFhNokJfrZrfezP9RtRa-F65ilUrEeZ15nVcB6ypX9P3Zo$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8SqJ5i9DYfttxr9F6YvXfVyCrV5cDroE-n5TCcr0qAvt= dGFhNokJfrZrfezP9RtRa-F65ilUrEeZ15nVcB6yOJPqcVs$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8SqJ5i9DYfttxr9F6YvXfVyCrV5cDroE-n5TCcr0qAvt= dGFhNokJfrZrfezP9RtRa-F65ilUrEeZ15nVcB6yC45enwE$=20

=3D =3D =3D
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FOUS30 KWBC 161944
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
244 PM EST Tue Dec 16 2025

Day 1
Valid 16Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PACIFIC NORTHWEST...

16z update:
The timing/placement of the quick hitting A.R. surge remains on
track with re-invigoration of the NW California portion will
generally start around 20-21z before expanding northward with the
core of the northern stream southwesterly deep jet streak reaching
NW Oregon just before 06z. IVT values are well above normal due to
the strength of deep layer flow, peaking near 900 kg/m/s. The
duration of the core of the AR surge will likely be ending about
12z-15z. Additional 1-2" for the lower coastal ranges are expected
with spots of 2-3" in the mid-slopes of the Cascade, Olympic ranges
with only a few highest peaks near the Klamath Range near 4" by
12z. As such, no changes were made to the broad Marginal Risk of
Excessive Rainfall.

Gallina

~~~~Prior Discussion~~~~
Maintained the previously issued Marginal Risk area from
Washington southward along the Cascades and the coastal ranges into
northwest California today and tonight. Yet another round of
precipitation will be spreading from west to east across portions
of Washington and Oregon. Cooler air coming in behind the system
should result in mountain snows and rain for the lowlands and
mountain passes today into tonight. There should be a separate area
of mainly rain and some higher level snows that gets directed into
the southwest portion and northwest corner of California with
amounts locally enhanced by orographic influences. The previous
outlook largely covered this scenario so few changes were
needed.Once again...some overlap between the excessive rainfall
areas and mountain snowfall amounts was unavoidable but we tried to
keep the ERO away from the placement of the WPC Winter Weather
Desk snow amounts of 6 inches or greater.

The overall synoptic pattern continued to show the deepest moisture
and broadest coverage of rainfall arriving in association with the
surface cold front around 17/00Z and the diminishing QPF as the
area gets whisked eastward.

Bann

Day 2
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann/Kleebauer


Day 3
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER MUCH OF
WESTERN OREGON AND PORTIONS OF ADJOINING STATES...

20Z Update... Changes were minimal with the forecast remaining
steadfast through the 12z NWP suite. The threat for significant
rainfall remains elevated across the western half of Oregon with a
focal point centered over the southern Cascades and the adjacent
valleys on either side. The key in this threat is the projected
"spillover" of heavier precip to the leeward side of the Cascades
due to a pronounced 700mb jet protrusion inland from the Pacific
leading to significant Pacific moisture breaching the terrain and
allowing for heavier precip to make it downwind of the mountains.
This is the area where ARI forecasts are hovering between the
25-100 year exceedance intervals, matching the previous output from
overnight's forecast. This allowed for general continuity in the
SLGT risk area with modifications only made to match to the latest
QPF footprint with emphasis on where 2+" will fall in the D3 time
frame, especially away from the coastal plain.=20

Kleebauer

...Previous Forecast...

The next in a series of Atmospheric Rivers will arrive early
Thursday with its axis of greatest moisture transport being
directed primarily along the western coast of Oregon...with maximum
IVT values in excess of 800 kg per meter per second largely being
directed perpendicular into the coastal ranges early in the period.
Global models continue to advertise the possibility of 6 inches or
more of rainfall during the period...and comparing the WPC 24hr
QPF to ARI yielded a broad swath exceeding the 2-5 year return
intervals. It was also worth noting that the highest ARIs were just
to the east of the crest of the Cascades where an axis of 25-100
year exceedance intervals was depicted. This does seem like a
scenario where more spillover into the normally drier downslope
areas is plausible, so could be an impactful event even into some
of those areas. Consequently, the Day 3 excessive rainfall outlook
expanded the Slight Risk eastward in Oregon to cover areas with QPF
in excess of 5 inches and the highest ARI values mentioned above
given the concern for spillover. Snowfall within this area should
be confined to the higher elevations.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-ypAPJJuuaAwceezEnqnBKRX50q3ocr24Py2XIZ2prBU= Lh__nb7IrznLLio1RNCoUjxxupOwOEXC9ejVdRCDef3GmH0$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-ypAPJJuuaAwceezEnqnBKRX50q3ocr24Py2XIZ2prBU= Lh__nb7IrznLLio1RNCoUjxxupOwOEXC9ejVdRCDsnST7bY$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-ypAPJJuuaAwceezEnqnBKRX50q3ocr24Py2XIZ2prBU= Lh__nb7IrznLLio1RNCoUjxxupOwOEXC9ejVdRCDTu6tGL8$=20

=3D =3D =3D
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FOUS30 KWBC 162335
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
635 PM EST Tue Dec 16 2025

Day 1
Valid 01Z Wed Dec 17 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PACIFIC NORTHWEST...

Both the 18z HREF and 12z REFS paint a similar QPF picture through
12z. The threat of heavy rainfall across portions of northern=20
California continues through the period, while a renewed surge of=20
heavy rains impacting portions of WA early on shifts south across=20
western OR with time. IVT values are well above normal due to the=20
strength of deep layer flow, peaking near 900 kg/m/s. An additional
1-2" for the lower coastal ranges are expected with local amounts
to 4" across portions of the Olympics, Cascades, and terrain of
northern CA by 12z. Only cosmetic changes were made to the broad=20
Marginal Risk of Excessive Rainfall.

Roth


Day 2
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann/Kleebauer


Day 3
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER MUCH OF
WESTERN OREGON AND PORTIONS OF ADJOINING STATES...

20Z Update... Changes were minimal with the forecast remaining
steadfast through the 12z NWP suite. The threat for significant
rainfall remains elevated across the western half of Oregon with a
focal point centered over the southern Cascades and the adjacent
valleys on either side. The key in this threat is the projected
"spillover" of heavier precip to the leeward side of the Cascades
due to a pronounced 700mb jet protrusion inland from the Pacific
leading to significant Pacific moisture breaching the terrain and
allowing for heavier precip to make it downwind of the mountains.
This is the area where ARI forecasts are hovering between the
25-100 year exceedance intervals, matching the previous output from
overnight's forecast. This allowed for general continuity in the
SLGT risk area with modifications only made to match to the latest
QPF footprint with emphasis on where 2+" will fall in the D3 time
frame, especially away from the coastal plain.

Kleebauer

...Previous Forecast...

The next in a series of Atmospheric Rivers will arrive early
Thursday with its axis of greatest moisture transport being
directed primarily along the western coast of Oregon...with maximum
IVT values in excess of 800 kg per meter per second largely being
directed perpendicular into the coastal ranges early in the period.
Global models continue to advertise the possibility of 6 inches or
more of rainfall during the period...and comparing the WPC 24hr
QPF to ARI yielded a broad swath exceeding the 2-5 year return
intervals. It was also worth noting that the highest ARIs were just
to the east of the crest of the Cascades where an axis of 25-100
year exceedance intervals was depicted. This does seem like a
scenario where more spillover into the normally drier downslope
areas is plausible, so could be an impactful event even into some
of those areas. Consequently, the Day 3 excessive rainfall outlook
expanded the Slight Risk eastward in Oregon to cover areas with QPF
in excess of 5 inches and the highest ARI values mentioned above
given the concern for spillover. Snowfall within this area should
be confined to the higher elevations.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9yJ9QnzkUQBJ6OUonNg1PTGAxZ442AuYmIx86fXKyGQO= XutYRHqIveFmikdfWa17WGJxCsmCmWtYqMhKNt0BJA7vRRM$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9yJ9QnzkUQBJ6OUonNg1PTGAxZ442AuYmIx86fXKyGQO= XutYRHqIveFmikdfWa17WGJxCsmCmWtYqMhKNt0BUSkFoWs$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9yJ9QnzkUQBJ6OUonNg1PTGAxZ442AuYmIx86fXKyGQO= XutYRHqIveFmikdfWa17WGJxCsmCmWtYqMhKNt0Bw8fWyvM$=20

=3D =3D =3D
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FOUS30 KWBC 170823
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
323 AM EST Wed Dec 17 2025

Day 1
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.=20

Bann

Day 2
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER WESTERN
OREGON EXTENDING INTO A SMALL PORTION OF WASHINGTON AND
CALIFORNIA...

The next in a series of atmospheric rivers will arrive along the
west coast of North America early on Thursday. The threat for=20
significant rainfall remains elevated across the western half of=20
Oregon with a focal point for maximum precipitation centered over=20
the southern Cascades and the adjacent valleys on either
side...although a subtle northward shift was noted in the 17/00Z
guidance. The key in this threat is the projected "spillover" of=20
heavier precip to the leeward side of the Cascades due to a=20
pronounced 700mb jet from the Pacific leading to significant=20
Pacific moisture being drawn inland. This is the area where ARI=20
forecasts are hovering between the 25-100 year exceedance=20
intervals, matching the output from the past several model runs and deterministic QPF from WPC. As a result, Day 2 excessive rainfall
outlook was expanded the Slight Risk northward across portions of
the Washington Cascades in response to the subtle northward shift
noted earlier...with little reason to expand any farther eastward.

Bann

Day 3
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER=20
PORTIONS OF NORTHWEST CALIFORNIA...

The atmospheric river that came on-shore on Thursday will be on-
going across much of Oregon as the Day 3 period begins at 12Z on
Friday. A well-defined plume of deep layer moisture will continue
to be drawn from the eastern North Pacific Ocean eastward into
parts of the northern Great Basin by fast westerly flow aloft. IVT
values at or above 600 units is forecast to cover much of Oregon=20 initially...then weaken as the axis of the moisture plume and
associated precipitation settles into northern California. The
system looks to have trended a bit more progressive on Friday than
suggested by earlier runs...so some of the QPF values over Oregon
and northwest California have come down a bit. Even so...opted to
maintain a large amount of continuity with Slight Risk area over
northwest California and a portion of adjacent southwest Oregon
given the possibility of further wobbles in the placement of the
axis or variations in model QPF. As it stands...the area average=20 precipitation amounts are currently in the range of 1-2 inches=20
with localized higher amounts maxima in the terrain.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!99E-iz9V5MYM72IYJu3Tk0zY0uw23YmCltPqA4VKBowd= lWeNGN2Lvnew3yKA47WyYjJiFoG508eayEKfTNLFF-FZhhg$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!99E-iz9V5MYM72IYJu3Tk0zY0uw23YmCltPqA4VKBowd= lWeNGN2Lvnew3yKA47WyYjJiFoG508eayEKfTNLFKfFfDlU$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!99E-iz9V5MYM72IYJu3Tk0zY0uw23YmCltPqA4VKBowd= lWeNGN2Lvnew3yKA47WyYjJiFoG508eayEKfTNLF4TeqL_8$=20

=3D =3D =3D
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FOUS30 KWBC 171531
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1031 AM EST Wed Dec 17 2025

Day 1
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

...Middle Texas Coast...
A fairly defined southern stream shortwave is noted across the
Northwest Gulf with impressive shield expansion within the larger
scale diffluent flow. Strong southerly western Gulf LLJ initiated
thunderstorms along/parallel to the southern Texas coast and cold
pool interaction and deeper layer steering flow is allowing for cells/convective line to propagate eastward and remain well=20
offshore. However, as the upper- level cirrus shield clears to the=20
east, but low level moisture flux continues toward the Middle Texas
coast and coastal plain; insolation will allow for some increased=20
modest instability for an isolated thunderstorm or two to develop.=20
Cell motions will be very slow and may allow for longer duration=20
increased rainfall totals. Sandy soils will largely absorb these=20
modest rates/totals, but there remains a non-zero potential for=20
some flooding concerns particularly if the rates intersect with=20
poor drainage urban centers, though the coverage does not warrant=20
an increase in categorical level.

Gallina


Day 2
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER WESTERN
OREGON EXTENDING INTO A SMALL PORTION OF WASHINGTON AND
CALIFORNIA...

The next in a series of atmospheric rivers will arrive along the
west coast of North America early on Thursday. The threat for
significant rainfall remains elevated across the western half of
Oregon with a focal point for maximum precipitation centered over
the southern Cascades and the adjacent valleys on either
side...although a subtle northward shift was noted in the 17/00Z
guidance. The key in this threat is the projected "spillover" of
heavier precip to the leeward side of the Cascades due to a
pronounced 700mb jet from the Pacific leading to significant
Pacific moisture being drawn inland. This is the area where ARI
forecasts are hovering between the 25-100 year exceedance
intervals, matching the output from the past several model runs and deterministic QPF from WPC. As a result, Day 2 excessive rainfall
outlook was expanded the Slight Risk northward across portions of
the Washington Cascades in response to the subtle northward shift
noted earlier...with little reason to expand any farther eastward.

Bann

Day 3
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
PORTIONS OF NORTHWEST CALIFORNIA...

The atmospheric river that came on-shore on Thursday will be on-
going across much of Oregon as the Day 3 period begins at 12Z on
Friday. A well-defined plume of deep layer moisture will continue
to be drawn from the eastern North Pacific Ocean eastward into
parts of the northern Great Basin by fast westerly flow aloft. IVT
values at or above 600 units is forecast to cover much of Oregon initially...then weaken as the axis of the moisture plume and
associated precipitation settles into northern California. The
system looks to have trended a bit more progressive on Friday than
suggested by earlier runs...so some of the QPF values over Oregon
and northwest California have come down a bit. Even so...opted to
maintain a large amount of continuity with Slight Risk area over
northwest California and a portion of adjacent southwest Oregon
given the possibility of further wobbles in the placement of the
axis or variations in model QPF. As it stands...the area average
precipitation amounts are currently in the range of 1-2 inches
with localized higher amounts maxima in the terrain.

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9ie1hD08vWPSf3jPLJvpuTCkzAxDGoHTmB8Lpv2jyxul= 3NYywpKrwjd7jqy1RXMMFlC5GF6qVM9r-sIDtfgQKwniB_o$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9ie1hD08vWPSf3jPLJvpuTCkzAxDGoHTmB8Lpv2jyxul= 3NYywpKrwjd7jqy1RXMMFlC5GF6qVM9r-sIDtfgQYAgLknU$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9ie1hD08vWPSf3jPLJvpuTCkzAxDGoHTmB8Lpv2jyxul= 3NYywpKrwjd7jqy1RXMMFlC5GF6qVM9r-sIDtfgQUKufQV8$=20

=3D =3D =3D
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FOUS30 KWBC 172023
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
323 PM EST Wed Dec 17 2025

Day 1
Valid 16Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

...Middle Texas Coast...
A fairly defined southern stream shortwave is noted across the
Northwest Gulf with impressive shield expansion within the larger
scale diffluent flow. Strong southerly western Gulf LLJ initiated
thunderstorms along/parallel to the southern Texas coast and cold
pool interaction and deeper layer steering flow is allowing for cells/convective line to propagate eastward and remain well
offshore. However, as the upper- level cirrus shield clears to the
east, but low level moisture flux continues toward the Middle Texas
coast and coastal plain; insolation will allow for some increased
modest instability for an isolated thunderstorm or two to develop.
Cell motions will be very slow and may allow for longer duration
increased rainfall totals. Sandy soils will largely absorb these
modest rates/totals, but there remains a non-zero potential for
some flooding concerns particularly if the rates intersect with
poor drainage urban centers, though the coverage does not warrant
an increase in categorical level.

Gallina


Day 2
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER WESTERN
OREGON EXTENDING INTO A SMALL PORTION OF WASHINGTON AND
CALIFORNIA...

2000 UTC Update: Have added a 25% area -- which is an enhanced or=20
'higher- end' Slight Risk -- across eastern portions of the=20
Willamette Valley into the western slopes of the Cascades, while=20
also clipping the far eastern reaches of Portland metro along with=20
the western Columbia Gorge into far southern WA. The 12Z guidance=20
came in even wetter, owing to the strong AR which given better=20
sampling, the intensity of which is coming into better view now=20
within 24-36 hours of the main event. CW3E global ensemble guidance
(GEFS and ECENS) show peak IVT values ~1000 kg/m-s, while the=20
Western Region WRF mean peaks closer to 1200. Guidance QPFs show=20
widespread 4-8" amounts within 24hrs, with higher totals depicted=20
from the CAM (particularly in the 'enhanced' Slight Risk area). 12Z
HREF probabilities of QPF exceeding 5" within the Day 2 period are
90% or higher withing the enhanced Slight Risk area, while within=20
the same area, probabilities of exceeding 8" peak between 60-80+=20
percent. Both the HREF and RRFS show high probabilities of=20
0.50"+/hr rainfall rates between 16Z Wed through 12Z Thu (probs=20
over 50%; in many areas over 70-80%), with quite a bit of overlap=20
within the same areas through ~03Z Thu.=20

Therefore, the potential for small stream and/or river flooding=20
continues to increase with this event (per collaboration with the=20
National Water Center). However the potential for flash flooding=20
(more short-fused inundation), especially over burn scars, is also=20 increasing within the enhanced or 'higher-end' Slight Risk area.=20
Next shift will evaluate the potential need for a Moderate Risk.=20

Hurley
=20
Previous Discussion below...

The next in a series of atmospheric rivers will arrive along the=20
west coast of North America early on Thursday. The threat for=20
significant rainfall remains elevated across the western half of=20
Oregon with a focal point for maximum precipitation centered over=20
the southern Cascades and the adjacent valleys on either=20
side...although a subtle northward shift was noted in the 17/00Z=20
guidance. The key in this threat is the projected "spillover" of=20
heavier precip to the leeward side of the Cascades due to a=20
pronounced 700mb jet from the Pacific leading to significant=20
Pacific moisture being drawn inland. This is the area where ARI=20
forecasts are hovering between the 25-100 year exceedance=20
intervals, matching the output from the past several model runs and deterministic QPF from WPC. As a result, Day 2 excessive rainfall=20
outlook was expanded the Slight Risk northward across portions of=20
the Washington Cascades in response to the subtle northward shift=20
noted earlier...with little reason to expand any farther eastward.

Bann


Day 3
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
PORTIONS OF NORTHWEST CALIFORNIA...

The atmospheric river that came on-shore on Thursday will be on-
going across much of Oregon as the Day 3 period begins at 12Z on
Friday. A well-defined plume of deep layer moisture will continue
to be drawn from the eastern North Pacific Ocean eastward into
parts of the northern Great Basin by fast westerly flow aloft. IVT
values at or above 600 units is forecast to cover much of Oregon initially...then weaken as the axis of the moisture plume and
associated precipitation settles into northern California. The
system looks to have trended a bit more progressive on Friday than
suggested by earlier runs...so some of the QPF values over Oregon
and northwest California have come down a bit. Even so...opted to
maintain a large amount of continuity from the initial overnight
issuance with the Slight Risk area over northwest California and a
portion of adjacent southwest Oregon given the possibility of=20
further wobbles in the placement of the axis or variations in model
QPF. The only notable change for the 20z update was to expand the=20
slight risk eastward and more into the Trinity Mountains where QPF=20
values and snow levels are high. Area average precipitation=20
amounts are currently in the range of 1-2 inches with localized=20
higher amounts maxima in the terrain, some of which may fall as
snow.

Santorelli/Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5Aq_kH0Hoa5mggkNl__4_GgGtMdxGizZYCq8uXJw7zPI= wKshy5T910RvNmHmPJteGbKqHp1DNOvp2paSoXLSYWEOxGE$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5Aq_kH0Hoa5mggkNl__4_GgGtMdxGizZYCq8uXJw7zPI= wKshy5T910RvNmHmPJteGbKqHp1DNOvp2paSoXLSIxMep1I$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5Aq_kH0Hoa5mggkNl__4_GgGtMdxGizZYCq8uXJw7zPI= wKshy5T910RvNmHmPJteGbKqHp1DNOvp2paSoXLSUEUTZrk$=20

=3D =3D =3D
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FOUS30 KWBC 180025
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
725 PM EST Wed Dec 17 2025

Day 1
Valid 01Z Thu Dec 18 2025 - 12Z Thu Dec 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 2
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER WESTERN
OREGON EXTENDING INTO A SMALL PORTION OF WASHINGTON AND
CALIFORNIA...

2000 UTC Update: Have added a 25% area -- which is an enhanced or
'higher- end' Slight Risk -- across eastern portions of the
Willamette Valley into the western slopes of the Cascades, while
also clipping the far eastern reaches of Portland metro along with
the western Columbia Gorge into far southern WA. The 12Z guidance
came in even wetter, owing to the strong AR which given better
sampling, the intensity of which is coming into better view now
within 24-36 hours of the main event. CW3E global ensemble guidance
(GEFS and ECENS) show peak IVT values ~1000 kg/m-s, while the
Western Region WRF mean peaks closer to 1200. Guidance QPFs show
widespread 4-8" amounts within 24hrs, with higher totals depicted
from the CAM (particularly in the 'enhanced' Slight Risk area). 12Z
HREF probabilities of QPF exceeding 5" within the Day 2 period are
90% or higher withing the enhanced Slight Risk area, while within
the same area, probabilities of exceeding 8" peak between 60-80+
percent. Both the HREF and RRFS show high probabilities of
0.50"+/hr rainfall rates between 16Z Wed through 12Z Thu (probs
over 50%; in many areas over 70-80%), with quite a bit of overlap
within the same areas through ~03Z Thu.

Therefore, the potential for small stream and/or river flooding
continues to increase with this event (per collaboration with the
National Water Center). However the potential for flash flooding
(more short-fused inundation), especially over burn scars, is also
increasing within the enhanced or 'higher-end' Slight Risk area.
Next shift will evaluate the potential need for a Moderate Risk.

Hurley

Previous Discussion below...

The next in a series of atmospheric rivers will arrive along the
west coast of North America early on Thursday. The threat for
significant rainfall remains elevated across the western half of
Oregon with a focal point for maximum precipitation centered over
the southern Cascades and the adjacent valleys on either
side...although a subtle northward shift was noted in the 17/00Z
guidance. The key in this threat is the projected "spillover" of
heavier precip to the leeward side of the Cascades due to a
pronounced 700mb jet from the Pacific leading to significant
Pacific moisture being drawn inland. This is the area where ARI
forecasts are hovering between the 25-100 year exceedance
intervals, matching the output from the past several model runs and deterministic QPF from WPC. As a result, Day 2 excessive rainfall
outlook was expanded the Slight Risk northward across portions of
the Washington Cascades in response to the subtle northward shift
noted earlier...with little reason to expand any farther eastward.

Bann


Day 3
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
PORTIONS OF NORTHWEST CALIFORNIA...

The atmospheric river that came on-shore on Thursday will be on-
going across much of Oregon as the Day 3 period begins at 12Z on
Friday. A well-defined plume of deep layer moisture will continue
to be drawn from the eastern North Pacific Ocean eastward into
parts of the northern Great Basin by fast westerly flow aloft. IVT
values at or above 600 units is forecast to cover much of Oregon initially...then weaken as the axis of the moisture plume and
associated precipitation settles into northern California. The
system looks to have trended a bit more progressive on Friday than
suggested by earlier runs...so some of the QPF values over Oregon
and northwest California have come down a bit. Even so...opted to
maintain a large amount of continuity from the initial overnight
issuance with the Slight Risk area over northwest California and a
portion of adjacent southwest Oregon given the possibility of
further wobbles in the placement of the axis or variations in model
QPF. The only notable change for the 20z update was to expand the
slight risk eastward and more into the Trinity Mountains where QPF
values and snow levels are high. Area average precipitation
amounts are currently in the range of 1-2 inches with localized
higher amounts maxima in the terrain, some of which may fall as
snow.

Santorelli/Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-HOgv9M7e3nZ4pcsap5fDpS4JwT71sAS9RAqdViThRDt= XsRbQj5pk7LaLisjaPSIJhkz8ng6pybkEbqpXMzmmBl-DE4$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-HOgv9M7e3nZ4pcsap5fDpS4JwT71sAS9RAqdViThRDt= XsRbQj5pk7LaLisjaPSIJhkz8ng6pybkEbqpXMzmyK5ZSzE$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-HOgv9M7e3nZ4pcsap5fDpS4JwT71sAS9RAqdViThRDt= XsRbQj5pk7LaLisjaPSIJhkz8ng6pybkEbqpXMzmn2jAbs8$=20

=3D =3D =3D
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FOUS30 KWBC 180832
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
332 AM EST Thu Dec 18 2025

Day 1
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER=20
WESTERN OREGON EXTENDING INTO A SMALL PORTION OF WASHINGTON AND THE
NORTHWEST CORNER OF CALIFORNIA...

A well define plume of deep moisture will continue to approach the
coast and then progress inland bringing widespread coverage of=20
moderate or greater rainfall to portions of western Oregon and a=20
small part of adjacent Washington and the northwest corner of=20
California. After several runs where the guidance has shown a=20
subtle northward shift of the moisture plume and associated=20
rainfall...there was subtle shift southward in the latest suite of=20
guidance necessitating a small shift in the north/south position of
the Slight Risk along/near the Oregon Cascades. Overall...the risk
within the Slight Risk area remained along the west aspect of the=20
Cascades where the moisture plume encounters the Cascades and is=20
forced to lift orographically. Guidance showed widespread 3 inch to
6 inch precipitation amounts within 24hrs with isolated higher=20
totals depicted by the convective allowing models in and near the=20
terrain. Both the HREF and RRFS continued to show high=20
probabilities of 0.50"+/hr rainfall rates especially after 21Z=20
today which persists through 12Z Friday. Therefore, the potential=20
for small stream and/or river flooding continues to increase with=20
this event (per collaboration with the National Water Center).=20
However the potential for flash flooding (more short- fused=20
inundation), especially over burn scars, is also increasing.=20

Bann

Day 2
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER=20
PORTIONS OF NORTHWEST CALIFORNIA...

...Pacific Northwest...

The atmospheric river that came on-shore in the Day 1 period will=20
be on-going across Oregon...although the event should be winding=20
down in terms of rainfall rates and additional amounts fairly early
in the outlook period. A well-defined plume of deep layer moisture
will continue to be drawn from the eastern North Pacific Ocean=20
eastward into parts of the northern Great Basin by fast westerly=20
flow aloft. IVT values at or above 700 units are forecast to cover=20
much of Oregon initially...then weaken as the axis of the moisture=20
plume and associated precipitation settles into northern=20
California. Maintained a large amount of continuity in terms of=20
placement of the Slight Risk area clipping northwest California and
a portion of adjacent southwest Oregon.=20

Saw little reason to make any significant changes to the expanded
coverage of the Slight Risk area made yesterday to cover more into
the Trinity Mountains given latest QPF.=20

...Southern New England...
A trough crossing the eastern United States will draw increasing
amounts of moisture northward into parts of New England...helping
set the stage for locally heavy rainfall when flow aloft becomes
increasingly difluent and a surface warm front approaches from the
south early on Friday. WPC Deterministic QPF in the 1.0 to 1.4 inch
range is forecast along the track of the low. Offsetting the=20
potential of excessive rainfall by limiting rainfall rates/amount is
the meager instability expected to be in place.=20

Bann

Day 3
Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF=20
NORTHERN CALIFORNIA|...

Renewed rainfall is expected across northern California as yet=20
another push of moisture arrives on the heels of the AR which=20
departed during the day on Friday, The axis of the strongest on-=20
shore winds and the greatest on-shore moisture transport looks to=20
be south of the axis of the previous event, but there is likely to=20
be at least some overlap between the two rainfall footprints.=20
Precipitable water values increase to between 1.2 and 1.4 inches=20
along the northern California coast north of San Francisco south=20
of the Oregon/California border by early Saturday evening. Given=20
such high snow levels...there is not a lot of concern about=20
precipitation type until the moisture laden flow reaches the=20
northern end of the Sierra Nevada range (save for a few mountain=20
tops along the trajectory inland from the coast). With the areal=20
average amount of the rainfall forecast being in the 1 to 2 inch=20 range...will keep the Marginal Risk inherited from yesterdays Day=20
4 ERO and plan to adjust as needed when placement and amounts=20
become more locked in,

Bann

Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4EmAmY6NdM37RBWwn8UUmFrSqPU6s8VtD61HYYrDwPHJ= duHql51FXByo2be4Kk94uKCAJN7cqSzmnsDLQ80yBpC3Yhc$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4EmAmY6NdM37RBWwn8UUmFrSqPU6s8VtD61HYYrDwPHJ= duHql51FXByo2be4Kk94uKCAJN7cqSzmnsDLQ80y1hIU7OI$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4EmAmY6NdM37RBWwn8UUmFrSqPU6s8VtD61HYYrDwPHJ= duHql51FXByo2be4Kk94uKCAJN7cqSzmnsDLQ80yfhh5wHs$=20

=3D =3D =3D
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FOUS30 KWBC 181600
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1100 AM EST Thu Dec 18 2025

Day 1
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
WESTERN OREGON EXTENDING INTO A SMALL PORTION OF WASHINGTON AND THE
NORTHWEST CORNER OF CALIFORNIA...

16z update:=20
CIRA LPW and buoy observations denote the rapidly surging warm
front nearing the OR coast orienting from a developing sub 995mb
surface low southeast toward the OR/CA state-line. Mid to upper-
level 99th to record LPW values at 850-700 and 700-500mb have over-
run the coastal region but the very strong winds will reach the
area with the warm front. RAP, HRRR forecasts denote 60-80kts of
fairly unidirectional southwest flow from 925 to 700mb through the
core of the deep layer moisture. This brings IVT values to be over
1000 kg/m/s with some of the hi-res CAMS solutions nearing 1250
kg/m/s. As such, the orographic ascent will drive atypical
rain-rates for the mid to upper slopes of the coastal range and
central to northern Oregon Cascades, likely to be at or above
.5"/hr through the forecast period with averages around .75"/hr,
occasional up to 1" being possible. Localized totals of 6-8" are
probable with HREF probability near 80-100% for 8" for peaks of
eastern Linn/Marion counties.=20

While FFG values are high enough to accommodate the rates, totals=20
in the 6, 12 and 24hr rates are near exceedance and there are=20
places of 50 to 100 year Average Return Intervals (ARI), denoting=20
the uncommon nature to the rainfall rates/totals. However,=20
rain shadows will limit rainfall totals in the Willamette Valley,=20
the runoff should be high and swell rivers and streams fairly=20
quickly. Please refer to further river/stream forecasts from the=20
River Forecast Center and National Water Center. In collaboration=20
with the NWC, there are atypical response signals that would=20
suggest some rapid onset flooding in the upper reaches/extremities=20
of the watersheds. An upgrade to Moderate Risk was considered for=20
those upper- stretches in the Cascades but the areal extent is=20
considered to small to delineate.

Gallina



~~~~Prior Discussion~~~~
A well define plume of deep moisture will continue to approach the
coast and then progress inland bringing widespread coverage of
moderate or greater rainfall to portions of western Oregon and a
small part of adjacent Washington and the northwest corner of
California. After several runs where the guidance has shown a
subtle northward shift of the moisture plume and associated
rainfall...there was subtle shift southward in the latest suite of
guidance necessitating a small shift in the north/south position of
the Slight Risk along/near the Oregon Cascades. Overall...the risk
within the Slight Risk area remained along the west aspect of the
Cascades where the moisture plume encounters the Cascades and is
forced to lift orographically. Guidance showed widespread 3 inch to
6 inch precipitation amounts within 24hrs with isolated higher
totals depicted by the convective allowing models in and near the
terrain. Both the HREF and RRFS continued to show high
probabilities of 0.50"+/hr rainfall rates especially after 21Z
today which persists through 12Z Friday. Therefore, the potential
for small stream and/or river flooding continues to increase with
this event (per collaboration with the National Water Center).
However the potential for flash flooding (more short- fused
inundation), especially over burn scars, is also increasing.

Bann

Day 2
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
PORTIONS OF NORTHWEST CALIFORNIA...

...Pacific Northwest...

The atmospheric river that came on-shore in the Day 1 period will
be on-going across Oregon...although the event should be winding
down in terms of rainfall rates and additional amounts fairly early
in the outlook period. A well-defined plume of deep layer moisture
will continue to be drawn from the eastern North Pacific Ocean
eastward into parts of the northern Great Basin by fast westerly
flow aloft. IVT values at or above 700 units are forecast to cover
much of Oregon initially...then weaken as the axis of the moisture
plume and associated precipitation settles into northern
California. Maintained a large amount of continuity in terms of
placement of the Slight Risk area clipping northwest California and
a portion of adjacent southwest Oregon.

Saw little reason to make any significant changes to the expanded
coverage of the Slight Risk area made yesterday to cover more into
the Trinity Mountains given latest QPF.

...Southern New England...
A trough crossing the eastern United States will draw increasing
amounts of moisture northward into parts of New England...helping
set the stage for locally heavy rainfall when flow aloft becomes
increasingly difluent and a surface warm front approaches from the
south early on Friday. WPC Deterministic QPF in the 1.0 to 1.4 inch
range is forecast along the track of the low. Offsetting the
potential of excessive rainfall by limiting rainfall rates/amount is
the meager instability expected to be in place.

Bann

Day 3
Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA|...

Renewed rainfall is expected across northern California as yet
another push of moisture arrives on the heels of the AR which
departed during the day on Friday, The axis of the strongest on-
shore winds and the greatest on-shore moisture transport looks to
be south of the axis of the previous event, but there is likely to
be at least some overlap between the two rainfall footprints.
Precipitable water values increase to between 1.2 and 1.4 inches
along the northern California coast north of San Francisco south
of the Oregon/California border by early Saturday evening. Given
such high snow levels...there is not a lot of concern about
precipitation type until the moisture laden flow reaches the
northern end of the Sierra Nevada range (save for a few mountain
tops along the trajectory inland from the coast). With the areal
average amount of the rainfall forecast being in the 1 to 2 inch
range...will keep the Marginal Risk inherited from yesterdays Day
4 ERO and plan to adjust as needed when placement and amounts
become more locked in,

Bann

Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8VhHgc7dGAbypGrZt5UNCNJL7HUIKyV_OmII39rnb_mi= Z2Fy4RTt6hGe0D1ZE1pXYRF3gL6m2dm26TEC4phUVIUDDN8$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8VhHgc7dGAbypGrZt5UNCNJL7HUIKyV_OmII39rnb_mi= Z2Fy4RTt6hGe0D1ZE1pXYRF3gL6m2dm26TEC4phUU5vvSiY$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8VhHgc7dGAbypGrZt5UNCNJL7HUIKyV_OmII39rnb_mi= Z2Fy4RTt6hGe0D1ZE1pXYRF3gL6m2dm26TEC4phUlW5AGec$=20

=3D =3D =3D
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FOUS30 KWBC 182018
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
318 PM EST Thu Dec 18 2025

Day 1
Valid 16Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
WESTERN OREGON EXTENDING INTO A SMALL PORTION OF WASHINGTON AND THE
NORTHWEST CORNER OF CALIFORNIA...

16z update:
CIRA LPW and buoy observations denote the rapidly surging warm
front nearing the OR coast orienting from a developing sub 995mb
surface low southeast toward the OR/CA state-line. Mid to upper-
level 99th to record LPW values at 850-700 and 700-500mb have over-
run the coastal region but the very strong winds will reach the
area with the warm front. RAP, HRRR forecasts denote 60-80kts of
fairly unidirectional southwest flow from 925 to 700mb through the
core of the deep layer moisture. This brings IVT values to be over
1000 kg/m/s with some of the hi-res CAMS solutions nearing 1250
kg/m/s. As such, the orographic ascent will drive atypical
rain-rates for the mid to upper slopes of the coastal range and
central to northern Oregon Cascades, likely to be at or above
.5"/hr through the forecast period with averages around .75"/hr,
occasional up to 1" being possible. Localized totals of 6-8" are
probable with HREF probability near 80-100% for 8" for peaks of
eastern Linn/Marion counties.

While FFG values are high enough to accommodate the rates, totals
in the 6, 12 and 24hr rates are near exceedance and there are
places of 50 to 100 year Average Return Intervals (ARI), denoting
the uncommon nature to the rainfall rates/totals. However,
rain shadows will limit rainfall totals in the Willamette Valley,
the runoff should be high and swell rivers and streams fairly
quickly. Please refer to further river/stream forecasts from the
River Forecast Center and National Water Center. In collaboration
with the NWC, there are atypical response signals that would
suggest some rapid onset flooding in the upper reaches/extremities
of the watersheds. An upgrade to Moderate Risk was considered for
those upper- stretches in the Cascades but the areal extent is
considered to small to delineate.

Gallina



~~~~Prior Discussion~~~~
A well define plume of deep moisture will continue to approach the
coast and then progress inland bringing widespread coverage of
moderate or greater rainfall to portions of western Oregon and a
small part of adjacent Washington and the northwest corner of
California. After several runs where the guidance has shown a
subtle northward shift of the moisture plume and associated
rainfall...there was subtle shift southward in the latest suite of
guidance necessitating a small shift in the north/south position of
the Slight Risk along/near the Oregon Cascades. Overall...the risk
within the Slight Risk area remained along the west aspect of the
Cascades where the moisture plume encounters the Cascades and is
forced to lift orographically. Guidance showed widespread 3 inch to
6 inch precipitation amounts within 24hrs with isolated higher
totals depicted by the convective allowing models in and near the
terrain. Both the HREF and RRFS continued to show high
probabilities of 0.50"+/hr rainfall rates especially after 21Z
today which persists through 12Z Friday. Therefore, the potential
for small stream and/or river flooding continues to increase with
this event (per collaboration with the National Water Center).
However the potential for flash flooding (more short- fused
inundation), especially over burn scars, is also increasing.

Bann

Day 2
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
PORTIONS OF NORTHWEST CALIFORNIA...

20Z Update: Little deviation in the 12z model suite leading to
general run-to-run continuity across both New England and the
Western U.S for the respective ERO risks in place. Small
adjustments were made based on the QPF distribution and HREF
neighborhood probabilities from the latest numerical suite, but
changes were not enough to warrant any considerable detail in
either area. Best chance will likely lie within the coastal terrain
of northwestern CA where flow orthogonal to the terrain will
generate efficient upslope enhancement over the bulk of the period.=20

Kleebauer

..Previous Discussions..

...Pacific Northwest...

The atmospheric river that came on-shore in the Day 1 period will
be on-going across Oregon...although the event should be winding
down in terms of rainfall rates and additional amounts fairly early
in the outlook period. A well-defined plume of deep layer moisture
will continue to be drawn from the eastern North Pacific Ocean
eastward into parts of the northern Great Basin by fast westerly
flow aloft. IVT values at or above 700 units are forecast to cover
much of Oregon initially...then weaken as the axis of the moisture
plume and associated precipitation settles into northern
California. Maintained a large amount of continuity in terms of
placement of the Slight Risk area clipping northwest California and
a portion of adjacent southwest Oregon.

Saw little reason to make any significant changes to the expanded
coverage of the Slight Risk area made yesterday to cover more into
the Trinity Mountains given latest QPF.

...Southern New England...
A trough crossing the eastern United States will draw increasing
amounts of moisture northward into parts of New England...helping
set the stage for locally heavy rainfall when flow aloft becomes
increasingly diffluent and a surface warm front approaches from=20
the south early on Friday. WPC Deterministic QPF in the 1.0 to 1.4=20
inch range is forecast along the track of the low. Offsetting the=20
potential of excessive rainfall by limiting rainfall rates/amount=20
is the meager instability expected to be in place.

Bann


Day 3
Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA|...

20Z Update: The next stronger AR pulse from the Pacific will be=20
making headway into northern CA by the end of the period, but=20
persistence in the AR overall will maintain alignment from northern
Sierra over into the northern CA coast. Overall, the synoptic
pattern remains consistent in the evaluation of the run-to-run QPF
distribution with ensembles basically overlapping each other in
where the heavier precip will occur. The fortunate news is there is
still only a small axis of overlap from the previous period, so
cumulative impacts are less of a concern this go around. The urban
centers between Sacrament to San Francisco will be more at play
this period leading to maintenance of the MRGL over the I-80
corridor. Overall, changes were minimal with just some minor
adjustments on the northern and southern edges of the inherited
MRGL risk.=20

Kleebauer=20

..Previous Discussion..

Renewed rainfall is expected across northern California as yet
another push of moisture arrives on the heels of the AR which
departed during the day on Friday, The axis of the strongest on-
shore winds and the greatest on-shore moisture transport looks to
be south of the axis of the previous event, but there is likely to
be at least some overlap between the two rainfall footprints.
Precipitable water values increase to between 1.2 and 1.4 inches
along the northern California coast north of San Francisco south
of the Oregon/California border by early Saturday evening. Given
such high snow levels...there is not a lot of concern about
precipitation type until the moisture laden flow reaches the
northern end of the Sierra Nevada range (save for a few mountain
tops along the trajectory inland from the coast). With the areal
average amount of the rainfall forecast being in the 1 to 2 inch
range...will keep the Marginal Risk inherited from yesterdays Day
4 ERO and plan to adjust as needed when placement and amounts
become more locked in,

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7hjcXr5tNoy7vtk072XHeu2EQaFVEV0ioYYdkl78FhOD= d3NXk9zYIwXBxcApy71515RWE8pjJCdP6fPF2DtKIaUMHV0$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7hjcXr5tNoy7vtk072XHeu2EQaFVEV0ioYYdkl78FhOD= d3NXk9zYIwXBxcApy71515RWE8pjJCdP6fPF2DtKJ9DasXk$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7hjcXr5tNoy7vtk072XHeu2EQaFVEV0ioYYdkl78FhOD= d3NXk9zYIwXBxcApy71515RWE8pjJCdP6fPF2DtKq8_DjRY$=20

=3D =3D =3D
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FOUS30 KWBC 190048
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
748 PM EST Thu Dec 18 2025

Day 1
Valid 01Z Fri Dec 19 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
WESTERN OREGON EXTENDING INTO A SMALL PORTION OF WASHINGTON AND THE
NORTHWEST CORNER OF CALIFORNIA...

16z update:
CIRA LPW and buoy observations denote the rapidly surging warm
front nearing the OR coast orienting from a developing sub 995mb
surface low southeast toward the OR/CA state-line. Mid to upper-
level 99th to record LPW values at 850-700 and 700-500mb have over-
run the coastal region but the very strong winds will reach the
area with the warm front. RAP, HRRR forecasts denote 60-80kts of
fairly unidirectional southwest flow from 925 to 700mb through the
core of the deep layer moisture. This brings IVT values to be over
1000 kg/m/s with some of the hi-res CAMS solutions nearing 1250
kg/m/s. As such, the orographic ascent will drive atypical
rain-rates for the mid to upper slopes of the coastal range and
central to northern Oregon Cascades, likely to be at or above
.5"/hr through the forecast period with averages around .75"/hr,
occasional up to 1" being possible. Localized totals of 6-8" are
probable with HREF probability near 80-100% for 8" for peaks of
eastern Linn/Marion counties.

While FFG values are high enough to accommodate the rates, totals
in the 6, 12 and 24hr rates are near exceedance and there are
places of 50 to 100 year Average Return Intervals (ARI), denoting
the uncommon nature to the rainfall rates/totals. However,
rain shadows will limit rainfall totals in the Willamette Valley,
the runoff should be high and swell rivers and streams fairly
quickly. Please refer to further river/stream forecasts from the
River Forecast Center and National Water Center. In collaboration
with the NWC, there are atypical response signals that would
suggest some rapid onset flooding in the upper reaches/extremities
of the watersheds. An upgrade to Moderate Risk was considered for
those upper- stretches in the Cascades but the areal extent is
considered to small to delineate.

Gallina


~~~~Prior Discussion~~~~
A well define plume of deep moisture will continue to approach the
coast and then progress inland bringing widespread coverage of
moderate or greater rainfall to portions of western Oregon and a
small part of adjacent Washington and the northwest corner of
California. After several runs where the guidance has shown a
subtle northward shift of the moisture plume and associated
rainfall...there was subtle shift southward in the latest suite of
guidance necessitating a small shift in the north/south position of
the Slight Risk along/near the Oregon Cascades. Overall...the risk
within the Slight Risk area remained along the west aspect of the
Cascades where the moisture plume encounters the Cascades and is
forced to lift orographically. Guidance showed widespread 3 inch to
6 inch precipitation amounts within 24hrs with isolated higher
totals depicted by the convective allowing models in and near the
terrain. Both the HREF and RRFS continued to show high
probabilities of 0.50"+/hr rainfall rates especially after 21Z
today which persists through 12Z Friday. Therefore, the potential
for small stream and/or river flooding continues to increase with
this event (per collaboration with the National Water Center).
However the potential for flash flooding (more short- fused
inundation), especially over burn scars, is also increasing.

Bann

Day 2
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
PORTIONS OF NORTHWEST CALIFORNIA...

20Z Update: Little deviation in the 12z model suite leading to
general run-to-run continuity across both New England and the
Western U.S for the respective ERO risks in place. Small
adjustments were made based on the QPF distribution and HREF
neighborhood probabilities from the latest numerical suite, but
changes were not enough to warrant any considerable detail in
either area. Best chance will likely lie within the coastal terrain
of northwestern CA where flow orthogonal to the terrain will
generate efficient upslope enhancement over the bulk of the period.

Kleebauer

..Previous Discussions..

...Pacific Northwest...

The atmospheric river that came on-shore in the Day 1 period will
be on-going across Oregon...although the event should be winding
down in terms of rainfall rates and additional amounts fairly early
in the outlook period. A well-defined plume of deep layer moisture
will continue to be drawn from the eastern North Pacific Ocean
eastward into parts of the northern Great Basin by fast westerly
flow aloft. IVT values at or above 700 units are forecast to cover
much of Oregon initially...then weaken as the axis of the moisture
plume and associated precipitation settles into northern
California. Maintained a large amount of continuity in terms of
placement of the Slight Risk area clipping northwest California and
a portion of adjacent southwest Oregon.

Saw little reason to make any significant changes to the expanded
coverage of the Slight Risk area made yesterday to cover more into
the Trinity Mountains given latest QPF.

...Southern New England...
A trough crossing the eastern United States will draw increasing
amounts of moisture northward into parts of New England...helping
set the stage for locally heavy rainfall when flow aloft becomes
increasingly diffluent and a surface warm front approaches from
the south early on Friday. WPC Deterministic QPF in the 1.0 to 1.4
inch range is forecast along the track of the low. Offsetting the
potential of excessive rainfall by limiting rainfall rates/amount
is the meager instability expected to be in place.

Bann


Day 3
Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA|...

20Z Update: The next stronger AR pulse from the Pacific will be
making headway into northern CA by the end of the period, but
persistence in the AR overall will maintain alignment from northern
Sierra over into the northern CA coast. Overall, the synoptic
pattern remains consistent in the evaluation of the run-to-run QPF
distribution with ensembles basically overlapping each other in
where the heavier precip will occur. The fortunate news is there is
still only a small axis of overlap from the previous period, so
cumulative impacts are less of a concern this go around. The urban
centers between Sacrament to San Francisco will be more at play
this period leading to maintenance of the MRGL over the I-80
corridor. Overall, changes were minimal with just some minor
adjustments on the northern and southern edges of the inherited
MRGL risk.

Kleebauer

..Previous Discussion..

Renewed rainfall is expected across northern California as yet
another push of moisture arrives on the heels of the AR which
departed during the day on Friday, The axis of the strongest on-
shore winds and the greatest on-shore moisture transport looks to
be south of the axis of the previous event, but there is likely to
be at least some overlap between the two rainfall footprints.
Precipitable water values increase to between 1.2 and 1.4 inches
along the northern California coast north of San Francisco south
of the Oregon/California border by early Saturday evening. Given
such high snow levels...there is not a lot of concern about
precipitation type until the moisture laden flow reaches the
northern end of the Sierra Nevada range (save for a few mountain
tops along the trajectory inland from the coast). With the areal
average amount of the rainfall forecast being in the 1 to 2 inch
range...will keep the Marginal Risk inherited from yesterdays Day
4 ERO and plan to adjust as needed when placement and amounts
become more locked in,

Bann


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8kEiowoi34EB7SuOfWIt4TM9gmdvGOGoXGVs7UzuapeG= nsD8pK5zuuADPwQ58oKt4nttx4rlo0iQM6tk9oAlWSTLX-Y$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8kEiowoi34EB7SuOfWIt4TM9gmdvGOGoXGVs7UzuapeG= nsD8pK5zuuADPwQ58oKt4nttx4rlo0iQM6tk9oAlXypk4dY$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8kEiowoi34EB7SuOfWIt4TM9gmdvGOGoXGVs7UzuapeG= nsD8pK5zuuADPwQ58oKt4nttx4rlo0iQM6tk9oAl0dNd5Y0$=20

=3D =3D =3D
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FOUS30 KWBC 190829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
329 AM EST Fri Dec 19 2025

Day 1
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
PORTIONS OF NORTHWEST CALIFORNIA...

...Pacific Northwest...

Ongoing atmospheric river will drift southward while swift flow
aloft transports the plume of deep layer moisture into parts of=20
the northern Great Basin. IVT values at or above 700 units are=20
forecast to cover much of Oregon initially before it weakens as=20
the axis of the moisture plume and associated precipitation settles
into northern California. The Marginal Risk was maintained for
southwest Oregon and northern California, as well as the Slight
Risk over northwest California. Minimal adjustments were made to
account for the latest QPF trends and WPC forecast.

...Southern New England...

Locally heavy rainfall will be possible for portions of the
Northeast during this period as moisture drawn northward encounters
the advancing trough over the eastern states. With time the
the moist flow aloft becomes increasingly diffluent and a surface=20
warm front approaches from the south early on Friday. WPC=20
Deterministic QPF in the 1.0 to 1.4 inch range is forecast along=20
the track of the low. Offsetting the potential of excessive=20
rainfall by limiting rainfall rates/amount is the meager=20
instability expected to be in place. A Marginal Risk was maintained
from the New York/Connecticut/Massachusetts border to downeast=20
Maine.

Campbell/Bann


Day 2
Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF=20
NORTHERN CALIFORNIA|...

A relative lull in moisture surges expected during the majority of
this period before the next stronger atmospheric river from the=20
Pacific reaches northern California towards the end of Day 2.
Although there may be some overlap in heavy rainfall, the axis of=20
the strongest on-shore winds and the greatest on-shore moisture=20
transport looks to be south of the axis of the previous event.

Precipitable water values increase to between 1.2 and 1.4 inches=20
along the northern California coast north of San Francisco south of
the Oregon/California border by early Saturday evening. Given such
high snow levels...there is not a lot of concern about=20
precipitation type until the moisture laden flow reaches the=20
northern end of the Sierra Nevada range (save for a few mountain=20
tops along the trajectory inland from the coast). The urban centers
between Sacramento to San Francisco will be more at play this=20
period lead

Campbell/Bann


Day 3
Valid 12Z Sun Dec 21 2025 - 12Z Mon Dec 22 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
NORTHERN CALIFORNIA...

The Atmospheric River will strengthen over the northern half of
California resulting in scattered to widespread areas of enhanced
rainfall overlapping much of the same footprint from the Day 2
period. The latest guidance is suggesting daily accumulations of 3
to 7 inches, with 48 hour totals nearing 5 to 9 inches. A Slight=20
Risk is in effect from the West Coast to much of the Sierra Nevada=20
Range. There may be a need for an upgrade for portions of the=20
Sierra Nevada should guidance continue to increase over this area.

Campbell


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!63RNlJrYHmP3f7jP6XgvTdkqtm--4VWdNt_PWmJhN8Lt= ZjO1fZAJtb7fY_QzfvUsJfJxk4pPUFgv4LdICm2fCSKtfsk$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!63RNlJrYHmP3f7jP6XgvTdkqtm--4VWdNt_PWmJhN8Lt= ZjO1fZAJtb7fY_QzfvUsJfJxk4pPUFgv4LdICm2fKlJ7JEY$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!63RNlJrYHmP3f7jP6XgvTdkqtm--4VWdNt_PWmJhN8Lt= ZjO1fZAJtb7fY_QzfvUsJfJxk4pPUFgv4LdICm2ftX0Ce9k$=20

=3D =3D =3D
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FOUS30 KWBC 191556
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1056 AM EST Fri Dec 19 2025

Day 1
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL MAINLY OVER=20
PORTIONS OF NORTHWEST CALIFORNIA AND NEW ENGLAND...

The AR continues to sag southward, reduce residency time, as well
as generally weakening in flux intensity. All factors support a
reduction of the category to Marginal Risk for the remainder of the
day. Also, have removed the northern portions within Oregon
where even the northern edge of the AR plume has moved south
limiting rainfall totals to below excessive concerns.=20

Thinking and placement of the Marginal Risk in New England remains
on track; so no changes were made for this update.=20

Gallina



~~~~Prior Discussions~~~~
...Pacific Northwest...

Ongoing atmospheric river will drift southward while swift flow
aloft transports the plume of deep layer moisture into parts of
the northern Great Basin. IVT values at or above 700 units are
forecast to cover much of Oregon initially before it weakens as
the axis of the moisture plume and associated precipitation settles
into northern California. The Marginal Risk was maintained for
southwest Oregon and northern California, as well as the Slight
Risk over northwest California. Minimal adjustments were made to
account for the latest QPF trends and WPC forecast.

...Southern New England...

Locally heavy rainfall will be possible for portions of the
Northeast during this period as moisture drawn northward encounters
the advancing trough over the eastern states. With time the
the moist flow aloft becomes increasingly diffluent and a surface
warm front approaches from the south early on Friday. WPC
Deterministic QPF in the 1.0 to 1.4 inch range is forecast along
the track of the low. Offsetting the potential of excessive
rainfall by limiting rainfall rates/amount is the meager
instability expected to be in place. A Marginal Risk was maintained
from the New York/Connecticut/Massachusetts border to downeast
Maine.

Campbell/Bann


Day 2
Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA|...

A relative lull in moisture surges expected during the majority of
this period before the next stronger atmospheric river from the
Pacific reaches northern California towards the end of Day 2.
Although there may be some overlap in heavy rainfall, the axis of
the strongest on-shore winds and the greatest on-shore moisture
transport looks to be south of the axis of the previous event.

Precipitable water values increase to between 1.2 and 1.4 inches
along the northern California coast north of San Francisco south of
the Oregon/California border by early Saturday evening. Given such
high snow levels...there is not a lot of concern about
precipitation type until the moisture laden flow reaches the
northern end of the Sierra Nevada range (save for a few mountain
tops along the trajectory inland from the coast). The urban centers
between Sacramento to San Francisco will be more at play this
period lead

Campbell/Bann


Day 3
Valid 12Z Sun Dec 21 2025 - 12Z Mon Dec 22 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
NORTHERN CALIFORNIA...

The Atmospheric River will strengthen over the northern half of
California resulting in scattered to widespread areas of enhanced
rainfall overlapping much of the same footprint from the Day 2
period. The latest guidance is suggesting daily accumulations of 3
to 7 inches, with 48 hour totals nearing 5 to 9 inches. A Slight
Risk is in effect from the West Coast to much of the Sierra Nevada
Range. There may be a need for an upgrade for portions of the
Sierra Nevada should guidance continue to increase over this area.

Campbell


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8I1bOP78mjc5Y6TxqSkNoQmxhNJfOTO-PkXJWn7f8xQk= omEKxhAhHaI54s_eRQCoC8KurMCTvwvlFbb3Idq6wY8n7bU$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8I1bOP78mjc5Y6TxqSkNoQmxhNJfOTO-PkXJWn7f8xQk= omEKxhAhHaI54s_eRQCoC8KurMCTvwvlFbb3Idq6X6-TBaY$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8I1bOP78mjc5Y6TxqSkNoQmxhNJfOTO-PkXJWn7f8xQk= omEKxhAhHaI54s_eRQCoC8KurMCTvwvlFbb3Idq60Vqfljo$=20

=3D =3D =3D
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FOUS30 KWBC 192041
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
341 PM EST Fri Dec 19 2025

Day 1
Valid 16Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL MAINLY OVER
PORTIONS OF NORTHWEST CALIFORNIA AND NEW ENGLAND...

The AR continues to sag southward, reduce residency time, as well
as generally weakening in flux intensity. All factors support a
reduction of the category to Marginal Risk for the remainder of the
day. Also, have removed the northern portions within Oregon
where even the northern edge of the AR plume has moved south
limiting rainfall totals to below excessive concerns.

Thinking and placement of the Marginal Risk in New England remains
on track; so no changes were made for this update.

Gallina



~~~~Prior Discussions~~~~
...Pacific Northwest...

Ongoing atmospheric river will drift southward while swift flow
aloft transports the plume of deep layer moisture into parts of
the northern Great Basin. IVT values at or above 700 units are
forecast to cover much of Oregon initially before it weakens as
the axis of the moisture plume and associated precipitation settles
into northern California. The Marginal Risk was maintained for
southwest Oregon and northern California, as well as the Slight
Risk over northwest California. Minimal adjustments were made to
account for the latest QPF trends and WPC forecast.

...Southern New England...

Locally heavy rainfall will be possible for portions of the
Northeast during this period as moisture drawn northward encounters
the advancing trough over the eastern states. With time the
the moist flow aloft becomes increasingly diffluent and a surface
warm front approaches from the south early on Friday. WPC
Deterministic QPF in the 1.0 to 1.4 inch range is forecast along
the track of the low. Offsetting the potential of excessive
rainfall by limiting rainfall rates/amount is the meager
instability expected to be in place. A Marginal Risk was maintained
from the New York/Connecticut/Massachusetts border to downeast
Maine.

Campbell/Bann


Day 2
Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA|...

20Z Update: Continuity from the previous forecast was maintained as
12z model suite continued to project similar results from earlier
runs leading to little/no variability in the forecast. Expecting
areas within the northern Sierra Nevada to receive the most
appreciable precipitation given the trajectory of the IVT pulse and
persistent 850-600mb moisture feed with added upslope components
near the terrain. Greatest flood concerns likely in the adjacent
foothills on the windward side of the Sierra's. Highest probs for

5" are across the I-80 corridor at the CA/NV border with the

highest terrain still likely to be snow, limiting the threat for
flash flooding for the period to more of a MRGL stance. Thus, kept
the previous forecast with no change.

Kleebauer

..Previous Discussion..

A relative lull in moisture surges expected during the majority of
this period before the next stronger atmospheric river from the
Pacific reaches northern California towards the end of Day 2.
Although there may be some overlap in heavy rainfall, the axis of
the strongest on-shore winds and the greatest on-shore moisture
transport looks to be south of the axis of the previous event.

Precipitable water values increase to between 1.2 and 1.4 inches
along the northern California coast north of San Francisco south of
the Oregon/California border by early Saturday evening. Given such
high snow levels...there is not a lot of concern about
precipitation type until the moisture laden flow reaches the
northern end of the Sierra Nevada range (save for a few mountain
tops along the trajectory inland from the coast). The urban centers
between Sacramento to San Francisco will be more at play this
period lead

Campbell/Bann


Day 3
Valid 12Z Sun Dec 21 2025 - 12Z Mon Dec 22 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
NORTHERN CALIFORNIA...

20Z Update: A more substantial IVT pulse will impact the northern
half of California come Sunday leading to overlap of impacted
areas from D2. Multi-day accumulations coupled with higher rates
will induce greater flash flood potential over a large area with
the greatest risk over the northern Sierra Nevada foothills.
Multi-day totals of 5-10" are still forecast in that region of the
state, enough to warrant a continuation of a SLGT risk with
probabilities approaching the higher end of the risk threshold as
of this time. There is an opportunity for an upgrade in the
following updates, so please stay tuned for the latest in this
evolving threat.=20

Kleebauer

..Previous Discussion..

The Atmospheric River will strengthen over the northern half of
California resulting in scattered to widespread areas of enhanced
rainfall overlapping much of the same footprint from the Day 2
period. The latest guidance is suggesting daily accumulations of 3
to 7 inches, with 48 hour totals nearing 5 to 9 inches. A Slight
Risk is in effect from the West Coast to much of the Sierra Nevada
Range. There may be a need for an upgrade for portions of the
Sierra Nevada should guidance continue to increase over this area.

Campbell


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8L034ioToXxna13oielQ6S959jlwKlp3N-7c9ObD5I-y= rvxMeVh7TynTYpl7O8qtk9POmu4C2HN1jWD9gPcYKFyb4nU$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8L034ioToXxna13oielQ6S959jlwKlp3N-7c9ObD5I-y= rvxMeVh7TynTYpl7O8qtk9POmu4C2HN1jWD9gPcYVrVGHhI$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8L034ioToXxna13oielQ6S959jlwKlp3N-7c9ObD5I-y= rvxMeVh7TynTYpl7O8qtk9POmu4C2HN1jWD9gPcYrso9V4U$=20

=3D =3D =3D
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FOUS30 KWBC 200001
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
701 PM EST Fri Dec 19 2025

Day 1
Valid 01Z Sat Dec 20 2025 - 12Z Sat Dec 20 2025

The probability of rainfall exceeding flash flood guidance is less=20
than 5 percent.=20

Kleebauer


Day 2
Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA|...

20Z Update: Continuity from the previous forecast was maintained as
12z model suite continued to project similar results from earlier
runs leading to little/no variability in the forecast. Expecting
areas within the northern Sierra Nevada to receive the most
appreciable precipitation given the trajectory of the IVT pulse and
persistent 850-600mb moisture feed with added upslope components
near the terrain. Greatest flood concerns likely in the adjacent
foothills on the windward side of the Sierra's. Highest probs for

5" are across the I-80 corridor at the CA/NV border with the

highest terrain still likely to be snow, limiting the threat for
flash flooding for the period to more of a MRGL stance. Thus, kept
the previous forecast with no change.

Kleebauer

..Previous Discussion..

A relative lull in moisture surges expected during the majority of
this period before the next stronger atmospheric river from the
Pacific reaches northern California towards the end of Day 2.
Although there may be some overlap in heavy rainfall, the axis of
the strongest on-shore winds and the greatest on-shore moisture
transport looks to be south of the axis of the previous event.

Precipitable water values increase to between 1.2 and 1.4 inches
along the northern California coast north of San Francisco south of
the Oregon/California border by early Saturday evening. Given such
high snow levels...there is not a lot of concern about
precipitation type until the moisture laden flow reaches the
northern end of the Sierra Nevada range (save for a few mountain
tops along the trajectory inland from the coast). The urban centers
between Sacramento to San Francisco will be more at play this
period lead

Campbell/Bann


Day 3
Valid 12Z Sun Dec 21 2025 - 12Z Mon Dec 22 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
NORTHERN CALIFORNIA...

20Z Update: A more substantial IVT pulse will impact the northern
half of California come Sunday leading to overlap of impacted
areas from D2. Multi-day accumulations coupled with higher rates
will induce greater flash flood potential over a large area with
the greatest risk over the northern Sierra Nevada foothills.
Multi-day totals of 5-10" are still forecast in that region of the
state, enough to warrant a continuation of a SLGT risk with
probabilities approaching the higher end of the risk threshold as
of this time. There is an opportunity for an upgrade in the
following updates, so please stay tuned for the latest in this
evolving threat.

Kleebauer

..Previous Discussion..

The Atmospheric River will strengthen over the northern half of
California resulting in scattered to widespread areas of enhanced
rainfall overlapping much of the same footprint from the Day 2
period. The latest guidance is suggesting daily accumulations of 3
to 7 inches, with 48 hour totals nearing 5 to 9 inches. A Slight
Risk is in effect from the West Coast to much of the Sierra Nevada
Range. There may be a need for an upgrade for portions of the
Sierra Nevada should guidance continue to increase over this area.

Campbell


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8P93n7_w_uvpLcaK-QK66PLA-iZ52Yy0jgv5QnGHhksC= RcvW6lm2B0cbskuOsinmMtWL9lkiSjL60Nczv3yUNmgFn5E$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8P93n7_w_uvpLcaK-QK66PLA-iZ52Yy0jgv5QnGHhksC= RcvW6lm2B0cbskuOsinmMtWL9lkiSjL60Nczv3yUKlzJxXk$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8P93n7_w_uvpLcaK-QK66PLA-iZ52Yy0jgv5QnGHhksC= RcvW6lm2B0cbskuOsinmMtWL9lkiSjL60Nczv3yUJqQZrok$=20

=3D =3D =3D
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FOUS30 KWBC 200809
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
309 AM EST Sat Dec 20 2025

Day 1
Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF=20
NORTHERN CALIFORNIA|...

Still expecting areas within the northern Sierra Nevada to receive
the most appreciable precipitation given the trajectory of the IVT
pulse and persistent 850-600mb moisture feed with added upslope=20
components near the terrain. Greatest flood concerns likely in the=20
adjacent foothills on the windward side of the Sierra Nevada.=20
Highest probs for >5" are across the I-80 corridor at the
California/Nevada border with the highest terrain still likely to=20
be snow, limiting the threat for flash flooding for the period to=20
that of a Marginal.=20

Campbell/Kleebauer


Day 2 Valid 12Z Sun Dec 21 2025 - 12Z Mon Dec 22 2025

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR=20
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...

A significant uptick in moisture will be surging into northern=20
California during this period within the reinforced atmospheric=20
river and will lead to widespread heavy rainfall and greater=20
threat for flash flooding, particularly for portions of the Sierra=20
Nevada foothills where multi-day totals of 5-10" are forecast. A=20
Moderate Risk area was raised for this period given more locations=20
will be at risk for rapid runoff and potential debris flows. The
areal extent of the Moderate will continue to be monitored and may
be adjusted with future updates.

Campbell


Day 3
Valid 12Z Mon Dec 22 2025 - 12Z Tue Dec 23 2025

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR=20
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...

The ongoing atmospheric river will persist while sinking a bit southward
toward central California, spreading rainfall further down the
Sierra Nevada Range and along the coastline. With the reduction of
rain on the northern periphery the threat for excessive rainfall
will remain at a Marginal level. A Moderate Risk was raised again
for much of the area identified during the day 2 period and for
locations a touch to the south. This part of the state is expected
to pick up another 3+ inches which will tip the 3 day accumulations
over 12 inches for some areas. Any additional rainfall will lead to
runoff and increase the potential for sloughing and debris flow
along the foothills/adjacent locations.


Campbell



Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4ubyWpg1eLt7L3sfkdeEMJwYVbfwht40GyPPHEx4CUcV= zt9VI1Wvi0CXWit7IBKFWHulLEqwCxfgUgwj2jAHhev0w1U$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4ubyWpg1eLt7L3sfkdeEMJwYVbfwht40GyPPHEx4CUcV= zt9VI1Wvi0CXWit7IBKFWHulLEqwCxfgUgwj2jAHcwWUork$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4ubyWpg1eLt7L3sfkdeEMJwYVbfwht40GyPPHEx4CUcV= zt9VI1Wvi0CXWit7IBKFWHulLEqwCxfgUgwj2jAH4aKqDd4$=20

=3D =3D =3D
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FOUS30 KWBC 201547
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1047 AM EST Sat Dec 20 2025

Day 1
Valid 16Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA|...

1600 UTC update...no changes made to the previous outlook for this
period.

Oravec



Previous discussion


Still expecting areas within the northern Sierra Nevada to receive
the most appreciable precipitation given the trajectory of the IVT
pulse and persistent 850-600mb moisture feed with added upslope
components near the terrain. Greatest flood concerns likely in the
adjacent foothills on the windward side of the Sierra Nevada.
Highest probs for >5" are across the I-80 corridor at the
California/Nevada border with the highest terrain still likely to
be snow, limiting the threat for flash flooding for the period to
that of a Marginal.

Campbell/Kleebauer


Day 2
Valid 12Z Mon Dec 22 2025 - 12Z Tue Dec 23 2025

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...

A significant uptick in moisture will be surging into northern
California during this period within the reinforced atmospheric
river and will lead to widespread heavy rainfall and greater
threat for flash flooding, particularly for portions of the Sierra
Nevada foothills where multi-day totals of 5-10" are forecast. A
Moderate Risk area was raised for this period given more locations
will be at risk for rapid runoff and potential debris flows. The
areal extent of the Moderate will continue to be monitored and may
be adjusted with future updates.

Campbell


Day 3
Valid 12Z Mon Dec 22 2025 - 12Z Tue Dec 23 2025

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...

The ongoing atmospheric river will persist while sinking a bit southward
toward central California, spreading rainfall further down the
Sierra Nevada Range and along the coastline. With the reduction of
rain on the northern periphery the threat for excessive rainfall
will remain at a Marginal level. A Moderate Risk was raised again
for much of the area identified during the day 2 period and for
locations a touch to the south. This part of the state is expected
to pick up another 3+ inches which will tip the 3 day accumulations
over 12 inches for some areas. Any additional rainfall will lead to
runoff and increase the potential for sloughing and debris flow
along the foothills/adjacent locations.


Campbell



Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!74i3h7JCLwOl9KFthRmO1cvG5EMATF901Ji8cJfGf48s= 2Udx9e-_u_ujoT-Ijgm4CCJkjzkn3c50MBu0uTY5c_5PT6w$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!74i3h7JCLwOl9KFthRmO1cvG5EMATF901Ji8cJfGf48s= 2Udx9e-_u_ujoT-Ijgm4CCJkjzkn3c50MBu0uTY5Ukr4iQU$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!74i3h7JCLwOl9KFthRmO1cvG5EMATF901Ji8cJfGf48s= 2Udx9e-_u_ujoT-Ijgm4CCJkjzkn3c50MBu0uTY5UvbbxJM$=20

=3D =3D =3D
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FOUS30 KWBC 202029
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
329 PM EST Sat Dec 20 2025

Day 1
Valid 16Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA|...

1600 UTC update...no changes made to the previous outlook for this
period.

Oravec


Previous discussion


Still expecting areas within the northern Sierra Nevada to receive
the most appreciable precipitation given the trajectory of the IVT
pulse and persistent 850-600mb moisture feed with added upslope
components near the terrain. Greatest flood concerns likely in the
adjacent foothills on the windward side of the Sierra Nevada.
Highest probs for >5" are across the I-80 corridor at the
California/Nevada border with the highest terrain still likely to
be snow, limiting the threat for flash flooding for the period to
that of a Marginal.

Campbell/Kleebauer


Day 2
Valid 12Z Sun Dec 21 2025 - 12Z Mon Dec 22 2025

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...

2030 UTC Update: Expanded the Slight and Moderate Risk areas based
on the latest (12Z) guidance QPFs and trends. Within the Moderate
Risk area, there are several hours of >50% HREF probabilities of=20
at least 0.50"/hr rates between 12Z Sun and 03Z Mon, while HREF
probabilities of >8" within the 24 hour Day 2 period are >60% for
much of the area.

Hurley

Previous Discussion..

A significant uptick in moisture will be surging into northern
California during this period within the reinforced atmospheric
river and will lead to widespread heavy rainfall and greater
threat for flash flooding, particularly for portions of the Sierra
Nevada foothills where multi-day totals of 5-10" are forecast. A
Moderate Risk area was raised for this period given more locations
will be at risk for rapid runoff and potential debris flows. The
areal extent of the Moderate will continue to be monitored and may
be adjusted with future updates.

Campbell


Day 3
Valid 12Z Mon Dec 22 2025 - 12Z Tue Dec 23 2025

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...

The ongoing atmospheric river will persist while sinking a bit southward
toward central California, spreading rainfall further down the
Sierra Nevada Range and along the coastline. With the reduction of
rain on the northern periphery the threat for excessive rainfall
will remain at a Marginal level. A Moderate Risk was raised again
for much of the area identified during the day 2 period and for
locations a touch to the south. This part of the state is expected
to pick up another 3+ inches which will tip the 3 day accumulations
over 12 inches for some areas. Any additional rainfall will lead to
runoff and increase the potential for sloughing and debris flow
along the foothills/adjacent locations.


Campbell



Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!92Pjj7SnoEKqf81z1OWmVFo25GzNuHrc74os4vgtGPQ2= Dk9CafhzCiDtlPk_RfSBwzymSC4PdOANe3Gd6BAURNSdpBM$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!92Pjj7SnoEKqf81z1OWmVFo25GzNuHrc74os4vgtGPQ2= Dk9CafhzCiDtlPk_RfSBwzymSC4PdOANe3Gd6BAUpwKLYqs$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!92Pjj7SnoEKqf81z1OWmVFo25GzNuHrc74os4vgtGPQ2= Dk9CafhzCiDtlPk_RfSBwzymSC4PdOANe3Gd6BAUPAGo5HU$=20

=3D =3D =3D
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