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Mesoscale Discussion 809
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   Mesoscale Discussion 0809
   NWS Storm Prediction Center Norman OK
   0802 PM CDT Sun May 21 2017

   Areas affected...South Texas

   Concerning...Severe potential...Watch possible 

   Valid 220102Z - 220330Z

   Probability of Watch Issuance...40 percent

   SUMMARY...A severe threat will be possible this evening across south
   Texas. Wind damage and isolated large hail will be the primary
   threats. Weather watch issuance could be needed across south Texas
   if the current severe threat increases.

   DISCUSSION...The latest surface analysis shows a 999 mb low in
   northern Mexico with a trough extending eastward from the low to
   near the Gulf Coast and then northward into south Texas. Low-level
   convergence appears to be maximized along the surface trough which
   is supporting thunderstorm development. Surface dewpoints in south
   Texas are in the lower to mid 70s F and MLCAPE is estimated to be in
   the 1500 to 2500 J/kg range. This combined with moderate deep-layer
   shear evident on regional WSR-88D VWPS and steep lapse rates will be
   favorable strong updrafts with isolated large hail potential. Backed
   surface winds to the east are also contributing to low-level shear
   which will could aide the developing of bowing structures with a
   wind damage threat. The bowing line segment that is near the Rio
   Grande River and is currently moving into south Texas at 25 to 30
   kt. This should keep any wind damage threat isolated. Nevertheless,
   trends will continue to be monitored and a weather watch is still
   being considered.

   ..Broyles/Hart.. 05/22/2017

   ...Please see for graphic product...


   LAT...LON   27099727 26759723 26309707 25949709 25879754 25929847
               26269908 27009962 27369954 27529912 27609778 27389721

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