SPC Nov 27, 2024 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0644 AM CST Wed Nov 27 2024

Valid 271300Z - 281200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER CENTRAL
MISSISSIPPI TO CENTRAL AND NORTHERN ALABAMA...AND PARTS OF THE
WESTERN/CENTRAL FLORIDA PANHANDLE TO SOUTHWESTERN GEORGIA...

...SUMMARY...
Isolated strong to severe storms are possible late tonight into
early Thanksgiving morning, over central Mississippi to central and
northern Alabama, and parts of the western/central Florida Panhandle
to southwestern Georgia.

...Synopsis...
A progressive, nearly zonal middle/upper-level pattern over much of
the CONUS will become more cyclonically curved east of the Rockies
through the period.  Contributing to this will be a positively
tilted shortwave trough -- evident in moisture-channel imagery from
central WY across northern parts of UT/NV.  This perturbation should
move rapidly across the central Rockies today, reaching southern
parts of KS and CO by 00Z.  The trough then should pivot east-
northeastward and elongate, reaching the Ohio Valley and Ozarks by
12Z tomorrow. 

11Z surface analysis showed an area of low pressure over the
northern TX Panhandle into northeastern NM, along and south of a
cold front extending into the Sangre de Cristos between RTN-TAD.  By
00Z, the low should consolidate and reach central or west-central
AR, with cold front southwestward across north-central and west-
central TX to southeastern NM.  The main low should redevelop to the
northeast over KY tonight, then move to a 12Z position roughly near
MGW, with cold front then extending to near the NC/TN line, northern
AL, south-central MS, southeastern LA, shelf waters off the middle/
upper TX Coast, to deep south TX. 

...MS/AL...
Widely scattered to scattered thunderstorms are expected to develop
near the cold front overnight -- most likely after 06Z -- with
marginal potential for a tornado, isolated damaging winds or severe
hail.

Despite the veered (southwesterly) surface flow ahead of the front,
a 40-50-kt west-southwesterly LLJ should contribute to long low-
level hodographs with some curvature.  That will foster 200-300 J/kg
effective and 0-1-km SRH values (locally higher), amidst 45-55-kt
effective-shear magnitudes and a narrow, front-parallel plume of
500-1000 J/kg MLCAPE.  However, with the veering prefrontal flow,
lift along the front will be compromised to some extent, causing
uncertainty on storm coverage.  Also, weak boundary-layer lapse
rates -- characteristic of this time of day in marginal-moisture
scenarios -- may yield long time windows for convective deepening,
potentially limiting storm strength at maturity if activity merges
with other precip or moves into weaker instability, as progged. 
Given these concerns, the threat continues to appear limited but
nonzero in nature, and has been removed from previous northwestern
areas where it now appears frontal passage will precede substantial
deep development. 

...Coastal FL Panhandle to southwestern GA...
Isolated to widely scattered thunderstorms are possible late
tonight, with a low-end but not negligible tornado and strong/
severe-gust threat.  

Development would be concentrated near a maximum in boundary-layer
lift accompanying southwest/northeast-oriented, low-level,
prefrontal confluence axis, undergoing theta-e advection from
favorably modifying maritime air on the north rim of the Loop
Current.  Modified forecast soundings show progressive lift and
erosion of a stable/capping layer from about 650-800 mb, located
beneath 500-1000 J/kg MLCAPE, as warm advection persists below that
stable layer and lift continues along the kinematic boundary.  This
may support development of a few thunderstorms after 06Z, with
enough low-level and deep shear on the east side of the boundary
(where surface winds will be relatively backed) to support supercell
potential, amidst roughly 40 kt effective-shear magnitudes and
100-150 J/kg of 0-1-km SRH.

..Edwards/Leitman.. 11/27/2024

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