SPC AC 260549

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1249 AM CDT Sat Sep 26 2020

   Valid 271200Z - 281200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER NORTHERN
   PORTIONS OF THE SOUTHERN PLAINS...OZARK PLATEAU...AND LOWER MO
   VALLEY...

   ...SUMMARY...
   Isolated severe thunderstorms are possible late Sunday afternoon
   through Sunday evening across northern portions of the southern
   Plains and adjacent Ozark Plateau.

   ...Synopsis...
   Overall upper pattern is expected to amplify significantly on Sunday
   as troughing deepens across the central CONUS and ridging builds
   over the western CONUS. The central CONUS deepening will be induced
   primarily by the progression of a strong shortwave trough from the
   northern Rockies into the central Plains. A cold front will begin
   the period extending southwestward from a low over south-central
   Ontario to another low in the central TX Panhandle.  
   Evolution of the previously mentioned shortwave trough (and
   accompanying cold air in its wake) will result in the
   southward/southeastward surge of this front, taking it through the
   mid MS Valley and majority of the southern Plains by early Monday
   morning. 

   Elsewhere, a weak upper low is forecast to be centered over the
   Mid-South early Sunday. This low is expected to transition to an
   open wave while accelerating northeastward over the Southeast and TN
   Valley ahead of amplifying upper trough over the Plains. 

   ...Southern Plains into the Ozark Plateau and Lower MO Valley...
   A warm and seasonally moist air mass is expected to be in place
   across the region ahead of the approaching cold front. These warm
   and moist low-levels beneath steep mid-level lapse rates favor
   strong buoyancy. However, warm mid-level temperatures and resulting
   convective inhibition introduce uncertainty regarding convective
   initiation within the open warm sector ahead the front. A more
   likely scenario is for storms to develop along the front, with the
   progressive, fast-moving character of the front then quickly
   undercutting any updrafts. Strengthening low-level southerly flow
   ahead of the front could also lead to additional post-frontal
   development. 

   All of these factors point to predominantly elevated storms. The
   vertical shear is expected to be strong enough to support rotation
   within the more robust updrafts, with an attendant threat for
   isolated severe hail. Given the strength of the low-level flow along
   and behind the front, convectively augmented downdrafts could be
   strong enough to result in a damaging wind gust or two.

   ...Southeast GA into Northern FL...
   Shortwave trough moving quickly across the Southeast and TN Valley
   is expected to result in scattered thunderstorms across portions of
   AL, GA, and northern FL. Enhanced mid-level flow throughout the base
   of this shortwave could result in a few more organized storms  and
   the potential for isolated damaging wind gusts. Uncertainty
   regarding the speed and strength of the shortwave as well as the
   degree of air mass destabilization results in too much uncertainty
   to introduce any probabilities with this outlook.

   ..Mosier.. 09/26/2020

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