SPC AC 210556

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1256 AM CDT Fri Apr 21 2023

   Valid 211200Z - 221200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF
   SOUTH AND EAST TX INTO THE LOWER MS VALLEY...AND ALSO FROM THE UPPER
   OH VALLEY INTO THE LOWER GREAT LAKES...

   ...SUMMARY...
   Isolated severe thunderstorms will be possible today across parts of
   the upper Texas coastal plain into the lower Mississippi Valley, and
   also across deep south Texas. Large hail and locally damaging gusts
   will be possible. A few strong storms capable of damaging gusts will
   also be possible across the upper Ohio Valley into the lower Great
   Lakes region.

   ...Synopsis...
   A deep longwave trough will remain in place across the central CONUS
   today. One embedded shortwave trough will move into Ontario from the
   upper Great Lakes region during the day today, while another
   embedded shortwave and attendant midlevel jet maximum move
   east-southeastward from the southern Plains toward the lower MS
   Valley. A deep-layer cyclone will move slowly eastward across the
   upper Great Lakes region, while one or more surface waves may
   develop along a cold front that will be draped from south TX into
   the lower MS Valley, OH Valley, and lower Great Lakes. 

   ...Parts of south and east TX into the lower MS Valley...
   Considerable uncertainty remains regarding the evolution of
   convection across TX into the lower MS Valley overnight, prior to
   the start of the forecast period at 12Z this morning. A weakening
   MCS may be ongoing near the upper TX and LA Gulf Coasts into the
   northwest Gulf of Mexico, with some potential for elevated
   redevelopment in the wake of the MCS. Steep midlevel lapse rates,
   moderate MUCAPE, and sufficient deep-layer shear will support some
   threat for hail and isolated damaging gusts with any stronger
   elevated convection during the morning. Wind profiles will remain
   favorable for organized storms through the day, so depending on the
   extent of destabilization this afternoon, isolated severe storms may
   redevelop from LA into MS along the front.  

   The environment farther southwest into deep south TX is likely to be
   relatively undisturbed by earlier convection, and moderate to strong
   buoyancy is likely to be in place during the afternoon. With
   generally weak surface convergence and limited large-scale ascent,
   storm coverage is expected to remain isolated at best, but
   sufficient deep-layer shear (with northwesterly flow aloft) will
   support a conditional risk for a supercell or two with large-hail
   potential. 

   ...Upper OH Valley into the lower Great Lakes region...
   Low-level moisture will remain limited from the OH Valley into the
   Great Lakes region, but relatively strong diurnal heating will
   support MLCAPE increasing into the 250-500 J/kg range this
   afternoon, with scattered thunderstorm development expected. Steep
   low-level lapse rates and modestly enhanced low-level flow will
   support the potential for isolated strong/damaging gusts before the
   threat diminishes with the onset of nocturnal cooling this evening.

   ..Dean/Bentley.. 04/21/2023

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