ACUS01 KWNS 271244
SWODY1
SPC AC 271243

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0643 AM CST Fri Dec 27 2024

Valid 271300Z - 281200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL GULF COAST STATES...

...SUMMARY...
A few strong to locally severe thunderstorms could occur today
across parts of the central Gulf Coast States.

...Synopsis...
In mid/upper levels, a broad area of cyclonic flow will persist
around mean troughing, from the Great Basin and Rockies across the
Great Plains to the Mississippi Valley.  The leading shortwave
trough -- in a series of them to influence convective potential
through early next week -- is apparent in moisture-channel imagery
over the MO Bootheel southward over portions of the Mid-South
region.  This feature will weaken considerably as it ejects
northeastward to OH by 00Z, in response to an upstream trough
initially over the southern/central Plains to Black Hills and
western Dakotas.  That higher-amplitude perturbation will reach the
eastern Dakotas, lower Missouri Valley and Ozarks by 00Z, then eject
northeastward to the Upper Great Lakes by the end of the period.  A
third shortwave trough -- currently moving inland from the Pacific
Northwest Coast -- should dig southeastward rapidly across the Great
Basin, reaching the southern High Plains and Permian Basin regions
by 12Z tomorrow.

At the surface, 11Z analysis showed a low over the western Ozarks
between SGF-HRO, with occluded front arching across the Mid-South to
west-central MS, warm front over south-central MS to near MOB then
southeastward across the FL Keys.  A slow-moving cold to
quasistationary front was drawn from west-central MS across the
southwestern LA coastline and TX shelf waters to a weak low over
Padre Island.  The low should move north-northeastward to northern
WI by 12Z tomorrow, with frontolysis occurring to its south near the
Mississippi Valley.  Cyclogenesis will occur overnight over
northwest TX in advance of the third mid/upper-level shortwave trough.

...Portions of central Gulf Coast region...
Multiple rounds of convection are expected through this evening,
with the best-organized cells offering locally strong-severe gusts
and a marginal tornado risk.  This includes a couple bands of
ongoing convection -- along a dominant western convergence zone just
ahead of the cold front, from eastern to southwestern MS and coastal
south-central LA, and another near I-59 in southern MS.  The 12Z LIX
sounding sampled the coastal airmass between these well, with MLCAPE
around 1400 J kg, effective SRH around 270 J/kg, modest winds
between 250-500 mb, and effective-shear magnitude near 30 kt.  With
the leading trough ejecting away from the area and weakening fast,
and the next remaining stronger but passing abeam of the outlook
area to the north, net height changes through most of the period
should be near neutral, with some rises possible in the near term
(indicating the ongoing activity is unlikely to get substantially
better organized than at present).

However, a progressive lobe of midlevel vorticity -- extending
southeastward from the second trough -- will foster large-scale
DCVA/lift late this afternoon into evening over portions of MS and
northern/western AL before the lobe ejects away and dissipates.
This will be well-timed with peak afternoon warming, to steepen
low-middle-level lapse rates and weaken MLCINH, contributing to
potential regeneration/strengthening of the western convective/
convergence band.  That process, with 60s F warm-sector surface
dewpoints between the cold and warm fronts, should contribute to
1000-2500 J/kg MLCAPE.  Deep shear and low-level hodographs should
favor at least isolated supercells, with 35-45-kt effective-shear
magnitudes and 200-300 J/kg effective SRH (maximized near the warm
front).  However, by mid/late afternoon, deep ascent and shear will
have peaked over most of the area.  With increasing displacement
between the stronger flow/forcing aloft related to the second
trough, and the favorable boundary-layer airmass, already marginal
severe potential should diminish overnight.

..Edwards/Grams.. 12/27/2024

$$
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