• Storm Prediction Center 31 07

    From LU9DCE@21:5/101 to ALERT on Wed Jul 31 04:24:11 2019
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    SPC 1200Z Day 1 Outlook
    Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1242
    AM CDT Wed Jul 31 2019
    Valid 311200Z - 011200Z
    ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
    THE MID-ATLANTIC TO NEAR NEW YORK CITY...
    ...SUMMARY... Thunderstorms associated with damaging wind gusts
    will be possible from parts of the Mid-Atlantic to near New York
    City this afternoon. A few severe storms will also be possible in
    the northern High Plains and lower to mid Missouri Valley.
    ...Mid-Atlantic into the Northeast... An upper-level trough will
    move across the eastern U.S. today. At the surface, a cold front will
    move southeastward toward the Mid-Atlantic as a pre-frontal trough
    strengthens during the day. Ahead of the front, surface dewpoints
    in the upper 60s to near 70 F will contribute to a pocket of moderate instability by midday. Thunderstorms are expected to develop in the
    foothills of the Appalachians, moving eastward toward the coastal
    areas during the afternoon. The moderate instability combined with
    steep low-level lapse rates should result in a wind-damage threat
    with the stronger multicell line segments. A slight risk is added
    to the outlook from the Mid-Atlantic northeastward to near New
    York City, where the potential appears the greatest for damaging
    wind gusts.
    ...Northern High Plains... An upper-level ridge will move
    slowly eastward across the northern High Plains today. At the
    surface, a cold front is forecast to move into eastern Montana and
    northwestern North Dakota. Ahead of this feature, a corridor of
    maximized low-level moisture will exist with surface dewpoints in
    the mid 60s F. In response, moderate instability should develop
    by midday. In spite of limited large-scale ascent, isolated
    thunderstorms should initiate along the front during the mid to late
    afternoon. Directional shear in the low to mid-levels and steep
    lapse rates should be enough for a marginal severe threat. Hail
    and strong gusty winds will be the primary threats.
    ...Lower to Mid Missouri Valley... Northwest mid-level flow
    will be in place across the central U.S. today. At the surface,
    a low will likely deepen across the central Plains as winds remain southeasterly across the lower to mid Missouri Valley. This will help
    a corridor of maximized low-level moisture to develop across eastern
    Kansas into southeast Nebraska, where moderate instability appears
    likely by afternoon. Model forecasts develop convection near a minor
    shortwave trough along the eastern edge of instability during the
    late afternoon and early evening. Convection will be mostly likely
    from near Omaha southward to near the Kansas City Metro early this
    evening. Moderate to strong deep-layer shear and steep mid-level
    lapse rates should result in a marginal hail threat. A few damaging
    wind gusts will be possible as well.
    ..Broyles/Bentley.. 07/31/2019
    SPC 0600Z Day 2 Outlook
    Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 0100
    AM CDT Wed Jul 31 2019
    Valid 011200Z - 021200Z
    ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS
    OF THE NORTHERN AND CENTRAL PLAINS...
    ...SUMMARY... Isolated strong to severe thunderstorms may occur
    across parts of the northern and central Plains on Thursday.
    ...Synopsis... A convectively enhanced mid-level perturbation will
    likely move around the apex of an upper ridge centered over the
    Southwest and southern Plains on Thursday. This perturbation should
    encourage convective development across parts of the northern/central
    High Plains Thursday afternoon. Farther east, an upper trough will
    move eastward off the East Coast and over the Canadian Maritimes.
    At the surface, a cold front will decelerate and become nearly
    stationary across parts of the Southeast by Thursday afternoon. At
    least scattered thunderstorms should form along/ahead of the front,
    but weak shear will likely preclude an organized severe threat
    across this region.
    Across the central Plains, a surface low should gradually deepen
    over western/central KS through the day. A baroclinic zone will
    likely reach across KS to the north and east of the low. A separate
    weak surface boundary should also be present across parts of the
    northern Plains. This front will probably extend from eastern MT
    into ND and perhaps northern MN by Thursday evening.
    ...Central Plains... Mainly elevated convection should be ongoing
    Thursday morning across eastern KS into western MO in a low-level
    warm air advection regime. These storms should quickly weaken
    as a low-level jet diminishes through the morning. Farther west,
    modest low-level upslope flow across parts of the central High Plains
    and weak ascent associated with the previously mentioned mid-level
    perturbation should initiate convection across the higher terrain
    of CO and southeastern WY by Thursday afternoon. As this activity
    spreads eastward into the central High Plains, it should encounter
    a weak to moderately unstable airmass along/south of a baroclinic
    zone. Even though mid-level westerly flow is not forecast to be
    overly strong across this region, a veering wind profile from the
    surface through mid levels should result in enough shear to support
    some updraft organization. Isolated large hail and damaging winds
    may occur with the strongest storms.
    Convective initiation along a baroclinic zone across KS and
    southern NE Thursday afternoon appears highly uncertain due to
    capping issues. But, any storm that develops would be capable of
    producing severe hail/wind given strong instability and sufficient
    shear forecast. A southerly low-level jet is expected to rapidly
    strengthen to around 35-40 kt Thursday evening across KS into
    southern NE. Robust convection appears likely along and north of
    the surface boundary in response. Moderate to locally strong MUCAPE
    and increasing shear should promote a risk for isolated large hail
    in the early, more discrete stage of storm development. There
    may also be a narrow window of opportunity for a tornado with
    any surface-based storms along the surface boundary from parts of
    north-central into northeastern KS early Thursday evening as the
    low-level jet strengthens.
    ...Northern Plains... Isolated to widely scattered storms should
    form by Thursday afternoon along a weak surface boundary extending
    west to east across parts of the northern Plains. Although mid-level west-northwesterly flow should be limited to no more than 20-25 kt,
    a moist low-level airmass to the south of this front will become
    moderately to strongly unstable by peak afternoon heating. Loosely
    organized thunderstorm clusters appear possible, and strong to
    damaging winds may occur as storms develop east-southeastward in
    a well-mixed boundary layer with steepened low-level lapse rates.
    Marginally severe hail may also be noted with the strongest cores.
    ...MAXIMUM RISK BY HAZARD... Tornado: 2% - Marginal Wind:
    5% - Marginal Hail: 5% - Marginal
    ..Gleason.. 07/31/2019
    SPC Day 1 Fire Weather Outlook
    Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK
    0110 AM CDT Wed Jul 31 2019
    Valid 311200Z - 011200Z
    ...Synopsis... An upper-level ridge is centered over the southern
    Rockies with several mid-level shortwave troughs rounding the
    periphery of this ridge. One of these shortwave troughs will support
    isolated dry thunderstorms in portions of the northern Rockies with
    another leading to weak lee cyclogenesis in the central High Plains
    and thus the potential for elevated fire weather concerns.
    ...Central Idaho and southwest Montana... A similar pattern to the
    last 2 days will bring another round of mostly dry thunderstorms to
    central Idaho and southwest Montana this afternoon and evening. PWAT
    values will be between 0.5 and 0.75" with high cloud bases and storm
    speeds around 25 to 30 mph. Repeated days of convection across
    this region may have moistened fuels in some parts of the area,
    but a significant portion of the region likely still has receptive
    fuels for fire starts.
    ...TX/OK Panhandles into southwest Kansas... Weak lee cyclogenesis
    is expected in eastern Colorado/western Kansas this afternoon as
    a weak shortwave trough moves through Colorado. The strengthening
    pressure gradient as a result of this developing lee cyclone will
    lead to 15 to 20 mph winds from the northern Texas Panhandle into
    southwest Kansas. In addition to the breezy conditions, surface
    relative humidity is expected to be around 20 percent and a lack
    of recent rainfall has led to cured fine fuels across portions of
    the area. Therefore, an elevated fire weather area is justified to
    cover this threat.
    ..Bentley.. 07/31/2019
    ...Please see www.spc.noaa.gov/fire for graphic product...
    SPC Day 2 Fire Weather Outlook
    Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK
    0111 AM CDT Wed Jul 31 2019
    Valid 011200Z - 021200Z
    ...Synopsis... Thursday's pattern will be very similar to Wednesday
    with the potential for dry thunderstorms in central Idaho and
    southwest Montana and elevated fire weather conditions in the TX/OK
    Panhandles into southwest Kansas.
    ...Northeast Oregon, most of Iowa, and southwest Montana... Isolated
    dry thunderstorms will be possible Thursday afternoon and evening
    from northeast Oregon eastward into eastern Idaho and southwest
    Montana. These thunderstorms are expected to form in an environment
    with PWAT values between 0.5" and 0.75". There is some uncertainty
    regarding fuels after many days of thunderstorms across portions
    of this region. In addition, there is forecast uncertainty related
    to slightly deeper monsoon moisture trying to move northward into
    eastern portions of the isolated dry thunderstorm area and slightly
    slower storm speeds than previous days. Therefore, additional tweaks
    to the IsoDryT area may be needed in future outlooks.
    ...TX/OK Panhandles into southwest Kansas... A weak surface
    cyclone will be present Thursday morning in eastern Colorado/western
    Kansas. Some weak lee cyclogenesis is expected through the day which
    will lead to strengthening surface winds in portions of the southern
    High Plains. This may lead to elevated fire weather conditions in
    portions of the TX/OK Panhandles into southwest Kansas where wind
    speeds are expected to be around 15 to 20 mph with relative humidity
    around 20 percent.
    ...Northeast California, northwest Nevada, and far southern Oregon...
    Breezy and dry conditions are possible in northeast California and
    northwest Nevada into southern Oregon on Thursday afternoon/evening.
    However, wind speeds are only marginally elevated at this time,
    so did not include an elevated area with this outlook, but will
    continue to monitor forecast trends in future outlooks.
    ..Bentley.. 07/31/2019
    ...Please see www.spc.noaa.gov/fire for graphic product...

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