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Mesoscale Discussion 802
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   Mesoscale Discussion 0802
   NWS Storm Prediction Center Norman OK
   0346 PM CDT Sat May 20 2017

   Areas affected...Portions of south-central TX

   Concerning...Severe Thunderstorm Watch 253...

   Valid 202046Z - 202145Z

   The severe weather threat for Severe Thunderstorm Watch 253

   SUMMARY...Several supercells persist mainly across western portions
   of Severe Thunderstorm Watch 253, with an isolated large hail and
   damaging wind threat continuing. A southward expansion in area
   and/or an extension in time may be needed for some portions of the
   watch prior to its scheduled 22Z expiration.

   DISCUSSION...A cold front has made little southward progress across
   south-central TX this afternoon, with a very moist and unstable
   airmass present to the south of the front. The thermodynamic and
   kinematic environment remains favorable for sustained severe
   convection, and recent radar imagery shows several supercells across
   Frio, La Salle, and Dimmit counties in TX. Isolated large hail and
   damaging winds will be possible with this ongoing convection as it
   moves southeastward with time. Additional showers have formed across
   parts of deep south TX, and if this activity can strengthen, it may
   also pose some severe risk given the favorable environment. Latest
   short-term guidance continues to suggest ongoing supercells should
   develop southeastward off the front over the next several hours into
   more of south-central/deep south TX. Depending on radar trends
   through 22Z, a southward expansion in area and/or an extension in
   time may be needed for some portions of the Severe Thunderstorm

   ..Gleason.. 05/20/2017

   ...Please see for graphic product...


   LAT...LON   28290037 29380087 29619982 29589689 28649698 27629760
               27409818 27439954 27579962 27819994 28290037 

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