ACUS01 KWNS 101240
SWODY1
SPC AC 101239

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0639 AM CST Tue Dec 10 2024

Valid 101300Z - 111200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
THE CENTRAL GULF COAST REGION INTO CENTRAL/SOUTHERN GEORGIA AND THE
FLORIDA PANHANDLE...

...SUMMARY...
A few strong to severe thunderstorms are possible across portions of
the central Gulf Coast region into central/southern Georgia and the
Florida Panhandle through tonight.

...Synopsis...
In mid/upper levels, mean troughing over the central CONUS will
evolve from positively to near neutrally tilted through the period,
in conjunction with two predominant subsynoptic-scale processes:
1.  South-southeastward digging of a cyclone now over extreme
northern MB, reaching the MB/ON border east of Lake Winnipeg by 12Z
tomorrow;
2.  Eastward shift of a strong, basal shortwave trough -- now
evident in moisture-channel imagery over northern NM into
south-central AZ -- absorbing a weaker/trailing perturbation and
reaching from middle TN to central LA by the end of the period.

As this occurs, a surface cold front -- analyzed at 11Z from a low
near BNA southwestward across northwestern MS, central LA, middle TX
Coast, and deep south TX -- should extend from western PA across the
southern Appalachians and southwestern AL, to southeastern LA, by
00Z.  A low-level, prefrontal confluence/convergence zone may
intensify this evening and tonight over portions of the FL
Panhandle, southeastern AL and southwestern GA.  The cold front
should approach and perhaps overtake the confluence zone by 12Z, as
it reaches a position from central PA across the western Carolinas,
to near a MCN-AAF line, then over the northeastern/central Gulf.

...Southeast...
Widely scattered, ongoing thunderstorms clusters are apparent across
portions of southern MS into southeastern LA, with a marginal
potential for a brief tornado or strong-severe gust.  See SPC
mesoscale discussion 2255 for near-term coverage of this scenario.
Similarly sporadic, isolated and marginal tornado and severe-gust
potential will exist throughout today and tonight with convection
along and just ahead of the cold front, as well as slowly increasing
convective coverage from late afternoon through overnight in the
prefrontal convergence zone.  The warm-sector environment will
remain characterized by a nearly saturated boundary layer with
surface dewpoints commonly in the upper 60s to near 70 F along the
coast, to mid 60s well inland, amidst nearly moist-adiabatic
low-level lapse rates.  Somewhat greater boundary-layer instability
is possible this afternoon in the inflow to the near-frontal
convection, as modest heating occurs through cloud breaks.  That my
offset weak midlevel lapse rates enough to support peak MLCAPE
around 1000 J/kg from southeastern LA to south-central AL,
decreasing northeastward as well as eastward.  An axis of lesser
buoyancy -- with MLCAPE remaining in the 500-800 J/kg range, should
shift eastward tonight near the confluence line, in support of
convection there.

Deep shear should increase from late this afternoon through tonight
with the more neutral tilt of the larger-scale trough aloft, and
related tightening of the mid/upper height gradient over the warm
sector.  While strongest flow aloft will remain behind the front,
effective-shear magnitudes of 45-55 kt and elongated low-level
hodographs are forecast from the northeastern Gulf Coast to the
Carolinas.  As the basal shortwave trough approaches (but remains
behind the cold front), the LLJ should strengthen to 45-55 kt
tonight over southern GA, reaching 55-65 kt over eastern NC, with
lengthening but only somewhat curved low-level hodographs.  The
northeastward extent of the conditional severe potential may extend
into near-coastal SC/NC; however, poor low- and middle-level lapse
rates (with stable layers apparent in forecast soundings) are
precluding any expansion of unconditional probabilities
northeastward for this outlook cycle.  The main (yet marginal)
severe threat for the Carolinas still appears to hold off until
early day 2.

..Edwards/Jewell.. 12/10/2024

$$
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