SPC AC 220645

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0145 AM CDT Mon Mar 22 2021

   Valid 241200Z - 251200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM EASTERN
   TEXAS INTO THE LOWER MISSISSIPPI VALLEY...

   ...SUMMARY...
   Isolated severe thunderstorms are possible from eastern Texas into
   the Lower Mississippi Valley on Wednesday.

   ...Synopsis...

   There is still quite a bit of uncertainty and spread among various
   forecast guidance regarding Wednesday. A broad area of southwesterly
   flow will exist from the southern Plains eastward as a shortwave
   trough over the Upper Midwest weakens and spreads northeast into
   Canada, while another upper shortwave trough ejects eastward from
   the Four Corners to the southern Plains by Thursday morning. A
   surface trough will develop across central TX while a warm front
   lifts northward across LA/MS, and a broad warm sector centered on
   the Lower MS Valley will be characterized by mid to upper 60s
   dewpoints. The progression of the Texas surface trough/cold front
   and the Gulf coast warm front remain uncertain and will have
   implications for severe potential on Wednesday into early Thursday
   morning.

   ...Eastern TX to the Lower MS Valley...

   A strong warm advection regime will persist across the central Gulf
   Coast, and heavy rainfall will likely be the main hazard for the
   region during the Day 3 period. However, at least some
   low-end/isolated severe thunderstorm potential appears possible.
   Ongoing rain and isolated thunderstorms will persist through the
   period, limiting stronger heating during the day. However, mid/upper
   60s dewpoints beneath moderate midlevel lapse rates will support
   MLCAPE as high as 1000-2000 J/kg. At least some weak inhibition will
   persist given the lack of stronger heating, and weak subsidence
   between the two upper shortwave troughs may suppress organized
   severe potential for much of the day. Wind profiles will improve
   after peak heating, with effective shear greater than 40 kt
   forecast. Upper forcing will remain weak for most of the period
   until the western upper shortwave trough kicks out into the Plains
   during the last 3-6 hours of the period. As this occurs, a surface
   cold front will sharpen and shift east across central/eastern TX. 

   Overall, the thermodynamic and kinematic environment could support
   at least isolated severe potential with all hazards possible.
   However, expected heavy rain, weak forcing, and timing of mid/upper
   level and surface features is resulting in low confidence. For now,
   low-end Marginal severe probabilities will be introduced for a
   conditional threat for embedded supercell storms in areas of ongoing
   precipitation, from Wednesday afternoon into early Thursday morning.

   ..Leitman.. 03/22/2021

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