SPC AC 210550

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1150 PM CST Mon Nov 20 2023

   Valid 211200Z - 221200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   SOUTHERN ALABAMA AND THE WESTERN FLORIDA PANHANDLE AND SOUTHWEST
   GEORGIA...

   ...SUMMARY...
   A few tornadoes are possible across south Alabama and the Florida
   Panhandle, mainly during the morning into the afternoon. The
   potential for locally damaging winds and a couple brief tornadoes
   will shift farther north and east this afternoon into early morning
   Wednesday across most of Georgia, the Carolinas, and far southern
   Virginia.

   ...Southeastern US...

   Latest satellite imagery suggests center of upper low is located
   near JLN. This feature is forecast to eventually dig southeast
   toward the mid-South as a secondary 500mb speed max translates
   southeast across eastern OK into southern AR by the end of the
   period. Immediately downstream, a corridor of strong midlevel flow
   will extend across the lower MS Valley into the middle Atlantic. 

   00z model guidance suggests modest height falls will develop ahead
   of this trough with values approaching 90m in 12hr, especially
   across the northern middle Atlantic region. In response to this
   trough, a weak surface low will advance across the OH Valley into
   southeast lower MI by late afternoon; however, a secondary surface
   low should evolve along the southern fringe of the Appalachians then
   track northeast into the Delmarva by 22/12z. This secondary surface
   low will prove instrumental in allowing modified air mass to advance
   across the Carolinas during the latter half of the period, with even
   weak buoyancy likely developing farther north during the overnight
   hours.

   Late this evening, an extensive corridor of deep convection has
   evolved within a strongly diffluent high-level flow regime from
   western AL-southern MS-southeast LA-western Gulf Basin. This
   corridor should progress steadily east through sunrise and likely
   extend across much of AL into the MS delta region by the start of
   the period. Strong deep-layer flow/shear will support organized
   convection, and embedded supercells are likely along this band.
   Forecast soundings at the start of the period exhibit MLCAPE in
   excess of 500 J/kg within a very moist and poor-lapse
   rate-environment. NAM soundings for PNS and GZH at 12z display 0-3km
   SRH between 400-700 m2/s2. Large-scale forcing should encourage an
   organized band of convection to migrate east, but this activity
   should weaken a bit downstream as it encounters less buoyancy and
   weaker forcing over northern FL/southeast GA.

   During the latter half of the period, primarily after 06z,
   boundary-layer recovery is expected across coastal Carolinas such
   that buoyancy will become more supportive of deep updrafts. Strong
   shear will favor organized convection, along with some supercell
   potential. Forecast soundings are quite moist with poor lapse rates
   through 9km. This will limit instability but isolated damaging winds
   and/or a tornado seem possible with this activity.

   ..Darrow/Lyons.. 11/21/2023

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