SPC AC 181248

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0748 AM CDT Thu Mar 18 2021

   Valid 181300Z - 191200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THIS
   AFTERNOON/EVENING FOR PARTS OF NORTHEASTERN SC AND SOUTHERN NC...

   ...SUMMARY...
   Scattered severe thunderstorms are expected through this evening
   from north Florida and south Georgia northeastward into the
   Carolinas and extreme southeast Virginia. All severe hazards are
   possible. Other isolated severe storms are possible from southern
   Ohio into the central Appalachians.

   ...Southeast Atlantic states through this evening...
   In advance of a pronounced midlevel trough over the lower MS Valley,
   a surface cyclone will occlude across the OH Valley, and a surface
   cold front will move eastward from AL to GA this afternoon and
   across the Carolinas tonight.  In advance of the front, a
   pre-frontal band of convection persists this morning from southwest
   GA into the FL Panhandle.  Recent surface observations have revealed
   a mesolow with the convective cluster moving into southwest GA, and
   this may help maintain somewhat stronger vertical shear in the short
   term across southwest GA.  Otherwise, the pre-frontal storms are
   likely to develop east-northeastward through the morning across
   southern/eastern GA and extreme north FL, and then into the eastern
   Carolinas later this afternoon/evening.

   As a coastal front moves northward today, low-level moisture will
   spread inland just in advance of the storms, and combine with some
   daytime heating to support MLCAPE of 500-1000 J/kg.  Midlevel lapse
   rates are expected to remain rather modest, which will temper
   buoyancy, though CAPE will still be large enough given 0-1 km SRH of
   100-200 m2/s2 just ahead of the convection.  A few tornadoes, and
   perhaps an isolated strong tornado, along with damaging winds, will
   be the main threats.

   Farther inland across the Piedmont, there may be sufficient
   destabilization in a narrow corridor to support a couple of storm
   clusters/supercells this afternoon.  The stronger storms could
   evolve later this morning/afternoon from the ongoing convection
   across north GA.  Where sufficient buoyancy overlaps the more
   favorable/curved hodographs east of the mountains, a couple of
   tornadoes, damaging gusts and isolated large hail will all be
   possible this afternoon/evening.

   ...OH Valley this afternoon/evening...
   Near the weakening, occluded low, there could be pockets of surface
   heating this afternoon, on the nose of the midlevel dry slot.  With
   some surface heating and cool midlevel temperatures, buoyancy should
   become sufficient for a few strong-severe storms this afternoon. 
   This area will be on the northwest edge of the stronger flow/shear,
   where a mix of multicell clusters and low-end supercells will be
   possible.

   ..Thompson/Gleason.. 03/18/2021

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