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Mesoscale Discussion 1502
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   MESOSCALE DISCUSSION 1502
   NWS STORM PREDICTION CENTER NORMAN OK
   0201 PM CDT TUE JUL 21 2015

   AREAS AFFECTED...VIRGINIA TIDEWATER...SOUTHERN DELMARVA PENINSULA

   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

   VALID 211901Z - 212100Z

   PROBABILITY OF WATCH ISSUANCE...20 PERCENT

   SUMMARY...INTENSIFYING THUNDERSTORM ACTIVITY THROUGH 20-22Z MAY BE
   ACCOMPANIED BY AT LEAST LOCALIZED STRONG WIND GUSTS...IN ADDITION TO
   FREQUENT CLOUD TO GROUND LIGHTNING AND HEAVY RAINFALL.  ALTHOUGH A
   SEVERE WEATHER WATCH IS NOT CURRENTLY ANTICIPATED...TRENDS WILL
   CONTINUE TO BE MONITORED.

   DISCUSSION...ON THE NOSE OF STRONGER BOUNDARY LAYER HEATING AND
   MIXING TO THE LEE OF THE CENTRAL/SOUTHERN APPALACHIANS...A ZONE OF
   ENHANCED LOW-LEVEL WARM ADVECTION AND CONVERGENCE APPEARS TO BE
   DEVELOPING ACROSS THE VIRGINIA TIDEWATER.  THIS COULD BECOME THE
   FOCUS FOR INTENSIFYING THUNDERSTORM DEVELOPMENT THROUGH
   20-22Z...SUPPORTED BY FORCING ASSOCIATED WITH A SUBTLE/WEAK IMPULSE
   ON THE SOUTHERN FRINGE OF BROADER SCALE CYCLONIC MID-LEVEL FLOW
   ACROSS THE CENTRAL APPALACHIANS/MID ATLANTIC REGION.

   IN THE PRESENCE OF SEASONABLY HIGH MOISTURE CONTENT CHARACTERIZED BY
   PRECIPITABLE WATER IN EXCESS OF 2 INCHES...HEATING INTO THE 90S
   APPEARS TO BE CONTRIBUTING TO AT LEAST A POCKET OF MIXED LAYER CAPE
   ON THE ORDER OF 3000 J/KG.  ALTHOUGH MID TROPOSPHERIC LAPSE RATES
   ARE RATHER MODEST...AS STORMS INCREASE AND INTENSIFY...A COMBINATION
   OF HEAVY PRECIPITATION LOADING... DOWNWARD MIXING OF AMBIENT 30 KT
   WESTERLY FLOW /CURRENTLY AS LOW AS 700 MB/...AND SUB-CLOUD
   EVAPORATIVE COOLING MAY CONTRIBUTE TO A COUPLE OF STRONG DOWNBURSTS.

   CONSOLIDATION OF CONVECTION AND ASSOCIATED COLD POOLS INTO AN
   EVOLVING ORGANIZED THUNDERSTORM CLUSTER DOES NOT APPEAR ENTIRELY OUT
   OF THE QUESTION...PERHAPS IMPACTING MUCH OF THE HAMPTON ROADS AREA
   INTO THE SOUTHERN DELMARVA...BEFORE SPREADING OFFSHORE.

   ..KERR/CORFIDI.. 07/21/2015


   ATTN...WFO...AKQ...LWX...

   LAT...LON   38547796 38547724 38307673 38447571 38007517 37317516
               36797635 36917733 37637811 38167838 38547796 

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Page last modified: July 21, 2015
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