SPC AC 220829

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0229 AM CST Tue Dec 22 2020

   Valid 241200Z - 251200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS FAR EASTERN
   SC...COASTAL NC...AND FAR SOUTHEAST VA...

   ...SUMMARY...
   Isolated severe thunderstorms are possible across portions of the
   Florida Panhandle and adjacent southeast Alabama and southwest
   Georgia early Thursday. Severe thunderstorms are also expected
   across the Mid-Atlantic States Thursday afternoon and evening.

   ...Synopsis and Discussion...
   Deep upper troughing is forecast to extend from northwestern Ontario
   into central Mexico early Thursday morning. Strong flow aloft will
   extend throughout the periphery of this upper trough. Shortwave
   trough embedded within the base of this larger trough will likely be
   moving through the Ozark Plateau and southern Plains early Thursday
   morning. Continued eastward/northeastward progression of this
   shortwave is expected, with the parent upper trough also progressing
   eastward. Evolution of the embedded shortwave will help induce a
   neutral tilt to the upper trough by Thursday afternoon, and a
   slightly negative tilt and closed upper circulation over the OH
   Valley by late Thursday night/early Friday morning.

   The maturing process of the upper trough will also result in further
   strengthening of the winds throughout its periphery. By early Friday
   morning, 100+ kt 500-mb winds will likely extend from the mid MS
   Valley southeastward/eastward through the base of the trough over
   the Southeast and then back northeastward into the Northeast. Very
   intense low-level flow is also expected, with 60+ kt at 850-mb
   extending from the Carolinas through the Mid-Atlantic into Quebec. 

   Modest severe potential is anticipated early Thursday along and
   ahead of the across the FL Panhandle and southeast AL/southwest GA.
   In this region, modest instability and strong flow will likely
   support a few strong/severe storms. An additional area of
   potentially greater severe potential is expected farther north
   across the Mid-Atlantic. In this area, a deepening surface low and
   strong low-level flow will contribute to robust moisture return as
   well as large, looping low-level hodographs. Strong buoyancy is not
   expected, but given the very strong vertical shear, even modest
   surface-based instability will likely result in severe storms.
   Strong to severe storms along the front appear likely, with some
   potential for warm-sector storms as well. Given the anticipated
   kinematic environment, any deeper warm-sector storms would likely
   become supercellular.

   ..Mosier.. 12/22/2020

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