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Mesoscale Discussion 1594
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   MESOSCALE DISCUSSION 1594
   NWS STORM PREDICTION CENTER NORMAN OK
   0230 PM CDT THU AUG 21 2014

   AREAS AFFECTED...PARTS OF CNTRL/SERN PENNSYLVANIA...CNTRL/SRN NEW
   JERSEY...CNTRL/ERN MARYLAND...DELAWARE...N CNTRL VIRGINIA AND THE
   DISTRICT OF COLUMBIA

   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

   VALID 211930Z - 212130Z

   PROBABILITY OF WATCH ISSUANCE...20 PERCENT

   SUMMARY...THE RISK FOR STRONG TO SEVERE STORM DEVELOPMENT MAY
   INCREASE ACROSS PORTIONS OF THE NORTHERN MID ATLANTIC COAST
   REGION...PARTICULARLY NEAR/SOUTH OF PHILADELPHIA THROUGH THE 22-00Z
   TIME FRAME.  SOME UNCERTAINTY PERSISTS CONCERNING THE EXTENT OF THE
   SEVERE WEATHER POTENTIAL...BUT AN ISOLATED SUPERCELL OR TWO MAY NOT
   BE OUT OF THE QUESTION.  WHILE THE NEED FOR A WATCH CURRENTLY
   APPEARS UNLIKELY...TRENDS WILL CONTINUE TO BE CLOSELY MONITORED.

   DISCUSSION...BENEATH A LAYER OF MID-LEVEL DRYING...TO THE SOUTH AND
   SOUTHEAST OF AN ELONGATED CYCLONIC CIRCULATION OVER THE LOWER GREAT
   LAKES REGION...SCATTERED THUNDERSTORM DEVELOPMENT IS NOW WELL
   UNDERWAY EAST SOUTHEAST OF THE LOWER GREAT LAKES REGION...TOWARD THE
   NORTHERN MID ATLANTIC COAST.  MODELS SUGGEST THAT MID-LEVEL LAPSE
   RATES REMAIN GENERALLY WEAK...LIMITING CAPE FOR MIXED BOUNDARY LAYER
   PARCELS ACROSS THE REGION TO SEASONABLY MODEST VALUES ON THE ORDER
   OF 1000-1500 J/KG.  HOWEVER...30-40 KT WEST NORTHWESTERLY 500 MB
   FLOW ACROSS MUCH OF PENNSYLVANIA INTO NORTHERN MID ATLANTIC COASTAL
   AREAS DOES APPEAR TO BE CONTRIBUTING TO SUFFICIENT VERTICAL SHEAR
   FOR MID-LEVEL UPDRAFT ROTATION.

   WITH ADDITIONAL SURFACE HEATING...A CONTINUED GRADUAL
   INTENSIFICATION OF STRONGER CELLS APPEARS POSSIBLE AS ACTIVITY
   DEVELOPS EAST OF THE HIGHER TERRAIN TOWARD COASTAL AREAS.  A WEAK
   SURFACE LOW/WARM FRONTAL ZONE NEAR AND WEST THROUGH SOUTH OF THE
   PHILADELPHIA METRO AREA MAY PROVIDE THE FOCUS FOR THE STRONGEST
   /MOST CONCENTRATED ACTIVITY BY 23-00Z...WITH THE ENVIRONMENT AT
   LEAST MARGINALLY SUFFICIENT FOR SUPERCELLS.

   ..KERR/DIAL.. 08/21/2014


   ATTN...WFO...PHI...CTP...LWX...

   LAT...LON   40877803 40757526 40247407 39037516 38727630 38727694
               39267778 39497780 40107809 40877803 

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Page last modified: August 21, 2014
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