SPC AC 031256

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0656 AM CST Fri Dec 03 2021

   Valid 031300Z - 041200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   Isolated thunderstorms may develop this afternoon through overnight
   across parts of the southern Plains to Mid-South.

   ...Synopsis...
   In mid/upper levels, a long fetch of west-northwesterly to westerly
   northern-stream flow will persist from the Pacific Northwest across
   the northern Plains, Upper Midwest, Great Lakes and Northeast. 
   Through this period, the strongest height changes and shortwave
   activity will remain to the north over Canada, and to the northwest
   over the northeasternmost Pacific.  In the much slower southern
   stream, a shortwave trough now over parts of eastern NM and west TX
   should pivot east-northeastward to OK and the Arklatex region
   through 12Z tomorrow. Upstream, a weak shortwave trough/vorticity
   lobe now near SAN will move gradually east-northeastward to AZ.

   At the surface, 11Z analysis shows a cold front from a low near FNB
   southwestward over south-central KS, the west-central TX Panhandle,
   and northeastern NM.  The front should cross the central Plains and
   mid Mississippi Valley through the period, reaching OH, KY, AR, and
   north-central to southwest TX by 12Z tomorrow.

   ...Southern Plains to Mid-South...
   Isolated, episodic thunderstorms are possible mainly this afternoon
   through tonight across the outlook area.  With only weak deep-layer
   forcing and an immature moisture recovery in the return flow,
   buoyancy will be limited, with severe potential too minimal for an
   unconditional outlook.  A combination of warm advection in return
   flow, with gradual moisture increase as the upstream Gulf
   trajectories continue to modify, will yield increasing boundary-
   layer theta-e beneath a fairly stout layer of basal EML MLCINH. 
   Still, weak DCVA preceding the southeastern lobe of the
   aforementioned shortwave trough may overlap the warm advection
   enough to steepen lapse rates and remove MUCINH locally, supporting
   potential for deep convection over the warm sector.  Additional
   convective lift is expected near the front late.  Forecast soundings
   indicate that planar progs of 1000-1500 MUCAPE may overrepresent
   actual available buoyancy, due to the larger theta-e largely kept
   below the inversion layer, but sufficient buoyancy should develop to
   support isolated lightning in the outlook area.

   ..Edwards.. 12/03/2021

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