ACUS01 KWNS 011247
SWODY1
SPC AC 011245

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0745 AM CDT Mon Apr 01 2024

Valid 011300Z - 021200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PORTIONS
OF THE SOUTHERN PLAINS TO THE LOWER MISSOURI AND OHIO VALLEY
REGIONS...

...SUMMARY...
Severe thunderstorms are expected today into this evening within a
broad swath from the southern Plains to the lower Missouri and Ohio
Valley regions. Tornadoes (a few strong), destructive hail, and
damaging thunderstorm gusts all are possible.

...Synopsis...
The most important mid/upper-level feature for this forecast will be
a deep, positively tilted, synoptic-scale trough, initially
extending from the northern High Plains across UT to northern Baja.
Several shortwave troughs and vorticity lobes will traverse the
associated cyclonic flow, as the broader trough shifts eastward. By
the end of the period, the synoptic trough should extend from IA
across KS and the southern High Plains to far west TX and
northwestern MX. A lead shortwave perturbation -- evident in
moisture-channel imagery over the eastern AZ/western NM region and
southward into adjoining parts of MX -- will eject across the
southern High Plains today, reaching the TX Panhandle and western OK
by 00Z. This feature should proceed northeastward to parts of
northwestern MO and IA by 12Z tomorrow.

Surface analysis at 11Z showed a frontal-wave low over central KS,
with warm front to near a line from SZL-STL-ILN. The low should
migrate along the slowly northward-moving warm front to MO by 00Z,
with cold front southwestward across northwestern OK and the
northernmost TX Panhandle. A dryline -- drawn initially from the
low to the eastern TX Panhandle, near MAF, then southward into
northern Coahuila -- should shift eastward through the afternoon to west-central/southwestern OK, extending southward across the TX Hill
Country to near LRD. By 00Z, the warm front -- perhaps modulated on
the mesoscale by areas of precip -- should extend across northern
MO, central parts of IL/IN, to southern OH and parts of WV. A
secondary low may form near the front/dryline intersection over
western OK. By 12Z tomorrow, an elongated low-pressure area, with
more than one center, is possible from the main frontal inflection
over northeastern MO to central IN. The main cold front should
reach southwestern MO, southeastern OK, northwest TX, and
southeastern NM. To its southeast, a Pacific front should overtake
the dryline this evening and overnight, reaching western AR, the
Arklatex, east TX, and parts of deep south TX by the end of the
period.

...Southeastern KS and western Ozarks to central TX...
Scattered (OK/KS) to isolated (central TX) thunderstorms are
expected to develop this afternoon along/ahead of the dryline and
front, quickly becoming severe with all hazards possible. The hail
threat will be greatest during the first few hours, while tornado
potential ramps into a probable early-evening peak. Severe
downdraft gusts also are possible, given the strong available
buoyancy and fast cell motions expected.

By late afternoon, much of OK and southeastern KS will reside under
the left-exit region of a cyclonically curving jet streak, above
strong low-level moisture transport accompanying a 50-65-kt LLJ.
Initiation is expected as large-scale ascent preceding the lead
shortwave starts to impinge upon a favorably heated dryline and
moist sector, and the basal EML capping layer erodes. This may
occur earlier over the northern OK/KS part of the outlook near the
front. The environment will be favorable for frequent large hail
and occasional significant to giant hailstones from any sustained
supercells. MLCAPE of 2000-3000 J/kg is possible, amidst 60-75 kt effective-shear magnitudes. Forecast soundings indicate abundant
inflow-layer moisture content to supply the updrafts, long
hodographs commonly associated with significant hail (from right- or left-moving storms), as well as significant to giant hail in both
historic analog soundings and a 2D hail-model.

Though convective coverage may become densest north of the Red
River, the potential for longer-lasting discrete modes near and
south of the Red River conditionally favor isolated extreme hail
sizes even into north TX. Given mesoscale uncertainties and
inconsistent convection-allowing model signals regarding initiation
timing (which influences what low-level shear/hodograph space cells
will enter) and mature storm duration before upscale merging/linear
evolution occur, will hold hail probabilities at previous levels for
now. However, a "hail moderate" may become necessary in this region
if mesoscale trends and post-12Z/today guidance become better
focused on timing/density.

The geometry of the pattern aloft will compel a strong component of mid/upper-level flow parallel to the convective alignment,
encouraging eventual merging, training, and quasi-linear evolution.
How long that process will take is uncertain, and the line
ultimately may backbuild into central TX. Still, with LLJ-expanded
hodographs and surface-based inflow parcels available in the
early/mid evening, tornado potential (some strong) should exist with
any remaining discrete storms, as well as in embedded QLCS
mesocirculations. Severe potential should ramp down late tonight
(after about 06Z) over this region, but persist longer in the next
(below).

...Lower Missouri Valley to Ohio Valley...
Multiple episodes of strong-severe thunderstorm development are
expected this afternoon through tonight, each capable of all severe
hazards. The distribution of severe weather over this corridor may
be quite non-uniform/clustered, as mesoscale convective processes
and boundaries evolve. Strong tornadoes may occur over parts of MO
into central/southern IL while the afternoon/evening CAPE/shear
parameter space and frontal proximity encourage potential
development of at least a couple long-lasting supercells.
Severe to isolated giant hail also is possible, especially from
discrete supercells the western portion over MO/IL containing
steepest lapse rates, greatest CAPE, and similarly favorable
vertical wind profiles as the southern Plains area.

Moist advection should quickly boost boundary-layer mixing ratios
and dewpoints today, with surface dewpoints in the 60s common along
and south of the warm front by midafternoon. Peak/preconvective
MLCAPE should reach 2000-2500 J/kg south of the warm front over
parts of MO/IL/IN, diminishing to 1000-1500 J/kg from the
northeastern KY/southern OH area eastward. Effective-shear
magnitudes should range from near 60 kt over MO to 40-50 kt in
eastern parts of the outlook. An MCS may evolve this evening from
convection over MO and sweep east-northeastward on either side of
the warm front, reaching parts of IN/OH/northern KY late tonight
before weakening. Though moving into an airmass that will be
stabilizing near the surface -- with time and eastward extent --
such a complex may have enough forced ascent and downward momentum
transfer behind that to maintain organized wind-damage potential
over the Ohio Valley tonight.

..Edwards/Leitman.. 04/01/2024

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