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Mesoscale Discussion 818
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   Mesoscale Discussion 0818
   NWS Storm Prediction Center Norman OK
   0350 PM CDT Tue May 23 2017

   Areas affected...Portions of the FL Panhandle...southern and
   southeastern GA...and coastal SC/NC

   Concerning...Tornado Watch 257...258...

   Valid 232050Z - 232215Z

   The severe weather threat for Tornado Watch 257, 258 continues.

   SUMMARY...An isolated tornado and damaging wind threat continues
   across Tornado Watches 257/258. The prospect of downstream watch
   issuance into coastal NC is uncertain.

   DISCUSSION...Primary near-term severe threat will remain focused
   with a cluster of thunderstorms across southeastern GA in
   association with a strong 40+ kt southwesterly low-level jet. The
   airmass downstream of this cluster into coastal SC remains weakly
   unstable, with MLCAPE of 500-1000 J/kg present. Recent VWP from KCLX
   shows strongly veering winds with height supporting around 50 kt of
   0-6 km shear, and RAP Mesoanalysis estimates 200-300 m2/s2 of 0-1 km
   SRH is present across this region. This will support continued
   updraft organization and low-level rotation with the strongest
   updrafts, and isolated tornadoes/damaging winds will continue to be
   possible across southeastern GA into parts of coastal SC for at
   least the next several hours.

   Behind the ongoing convective cluster in southeastern GA, low-level
   winds have veered more to southwesterly in southern GA and much of
   the FL Panhandle to the south of a weak front evident in 20Z surface
   observations. This has reduced 0-1 km SRH per latest TLH VWP and RAP
   Mesoanalysis estimates. While a brief tornado cannot be ruled out in
   this region, it appears the overall severe threat is diminishing
   across Tornado Watch 257. If current radar trends continue, then
   Tornado Watch 257 will be allowed to expire at 22Z as scheduled. 

   Farther north across coastal NC, some increase in an isolated
   tornado/damaging wind threat should occur through the early evening
   as the low-level jet overspreads this area. The prospect for surface
   based-convection and related severe threat will likely remain
   confined to a small part of coastal NC, and the prospect for a
   downstream watch into this region remains unclear.

   ..Gleason.. 05/23/2017

   ...Please see for graphic product...


   LAT...LON   30258540 30678315 31468296 32658178 33977979 34737834
               34707779 34427729 33937781 33077913 32328032 31688102
               30748141 30368205 30068409 30008496 30258540 

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