Mesoscale Discussion 0676
   NWS Storm Prediction Center Norman OK
   0510 PM CDT Tue May 18 2021

   Areas affected...South TX

   Concerning...Severe potential...Watch possible 

   Valid 182210Z - 182345Z

   Probability of Watch Issuance...40 percent

   SUMMARY...A couple of supercells will be possible into early
   evening, with a conditional risk of all hazards. Watch issuance is
   possible soon.

   DISCUSSION...At 22Z, convection is trying to deepen along a surface
   boundary across Dimmit and Frio Counties, while a mature supercell
   is noted across the international border south of Del Rio. MLCAPE of
   2000-3000 J/kg and effective shear of 30-40 kt will favor a
   supercell risk with any convection that can become sustained along
   the boundary, though very dry midlevel air noted on WV imagery and a
   tendency for the boundary to undercut developing cells as it sags
   southward make it uncertain as to whether convection can mature. 

   If mature supercells can be sustained along the boundary, then the
   environment would pose a conditional threat of all hazards. Watch
   issuance is possible to cover this threat.

   ..Dean/Grams.. 05/18/2021

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...CRP...EWX...

   LAT...LON   28340030 28459956 28799880 28589838 28289832 27859857
               27639886 27549916 27489950 27539983 27609999 28340030