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Mesoscale Discussion 1258
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   Mesoscale Discussion 1258
   NWS Storm Prediction Center Norman OK
   0235 PM CDT Fri Jul 07 2017

   Areas affected...southeast OH...southwest PA...much of WV...western
   and northern VA

   Concerning...Severe Thunderstorm Watch 402...

   Valid 071935Z - 072100Z

   The severe weather threat for Severe Thunderstorm Watch 402

   SUMMARY...Swaths of wind damage from isolated 50-65 mph gusts are
   likely west of the spine of the Appalachians.  It is unclear how
   much of a severe risk will develop east of severe thunderstorm watch
   402.  An additional watch is possible (50%).

   DISCUSSION...Radar mosaic shows a forward propagating squall line
   with a bowing segment moving southeast at 40 kt over far
   southeastern OH with a MCV probably beginning to develop in
   east-central OH.  Surface observations from central OH have measured
   gusts in the 35-50 kt range during the past 1.5 hours.  Subjective
   surface analysis indicates a low-level moist axis extending
   northeast from northern Ky along the OH River Valley into southwest
   PA with 68-73 degree F surface dewpoints.  A slightly drier airmass
   (less buoyant) is located over the Shenandoah Valley with lower 60s
   dewpoints but 0-3 km lapse rates have steepened.  

   Current thinking is the squall line will move into the eastern
   portions of severe thunderstorm watch 402 over the next few hours. 
   An EXtension-in-Area (EXA) to the watch will likely be needed given
   the airmass recovery from Cumberland county, MD southward into
   Pocahontas county, WV.  Although short-term model guidance suggests
   an overall weakening in the convective line from the Cumberland
   county to Pocahontas county corridor, the airmass has destabilized
   east of the higher terrain.  The convective line will probably be
   maintained and may yield a localized to isolated risk for wind
   damage during the early evening across western and northern portions
   of VA.

   ..Smith.. 07/07/2017

   ...Please see for graphic product...


   LAT...LON   40238094 39537855 38557753 37357875 37208012 37668138
               39278276 40238094 

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