MESOSCALE DISCUSSION 1447
   NWS STORM PREDICTION CENTER NORMAN OK
   1236 PM CDT SAT JUL 20 2013

   AREAS AFFECTED...ERN PA...NJ...SERN NY...CT...RI...MA...SRN VT...SRN
   NH...SRN ME

   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

   VALID 201736Z - 201830Z

   PROBABILITY OF WATCH ISSUANCE...80 PERCENT

   SUMMARY...THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON
   ACROSS MUCH OF THE URBAN CORRIDOR...AND ADJACENT AREAS OF THE
   NORTHERN MID ATLANTIC REGION AND NEW ENGLAND...POSSIBLY AS EARLY AS
   THE 18-20Z TIME FRAME.  A FEW OF THESE ARE EXPECTED TO BECOME
   SEVERE...PARTICULARLY WITH THE RISK FOR POTENTIALLY DAMAGING WIND
   GUSTS...AND A WATCH LIKELY WILL BE ISSUED WITHIN THE NEXT HOUR OR
   SO.

   DISCUSSION...SURFACE HEATING IS MAXIMIZING WITHIN THE LEE SURFACE
   TROUGH ALONG THE URBAN CORRIDOR...FROM WASHINGTON D.C. AND BALTIMORE
   NORTHEASTWARD THROUGH PHILADELPHIA...NEW YORK AND BOSTON...WHERE
   TEMPERATURES ARE NOW IN THE 90S.  THIS IS CONTRIBUTING TO LARGE
   MIXED LAYER CAPE IN THE PRESENCE OF HIGH PRECIPITABLE WATER CONTENT
   NEAR 2 INCHES...WHICH INCLUDES SURFACE DEW POINTS IN THE LOWER 70S. 

   CONVERGENCE WITHIN THE SURFACE TROUGH CURRENTLY APPEARS WEAK...BUT
   ISOLATED STORM DEVELOPMENT ALONG IT DOES NOT APPEAR OUT OF THE
   QUESTION DURING THE NEXT FEW HOURS...AS SEASONABLY STRONG CYCLONIC
   FLOW GRADUALLY OVERSPREADS THE REGION.  A MORE PROMINENT FOCUS FOR
   STORM DEVELOPMENT MAY BE AN INITIAL CONVECTIVELY GENERATED BOUNDARY
   TO THE NORTH AND WEST...NOW EXTENDING FROM PORTIONS OF SOUTHEASTERN
   MAINE THROUGH SOUTHERN NEW HAMPSHIRE AND VERMONT...INTO AREAS
   NEAR/EAST AND SOUTH OF THE CATSKILLS AND POCONOS...AS IT CONTINUES A
   SLOW SOUTHEASTWARD PROGRESSION.  

   GIVEN THE THERMODYNAMIC PROFILES...SHEAR BENEATH 30-40+ KT WEST
   SOUTHWESTERLY 500 MB FLOW WILL BE SUPPORTIVE OF ORGANIZED SEVERE
   STORM DEVELOPMENT...PERHAPS INCLUDING ISOLATED SUPERCELLS.  THE RISK
   FOR DAMAGING WIND GUSTS APPEAR THE MOST PROMINENT THREAT IN MOST
   AREAS.

   ..KERR/EDWARDS.. 07/20/2013


   ATTN...WFO...CAR...GYX...BOX...OKX...ALY...PHI...BGM...CTP...
   LWX...

   LAT...LON   38987703 39887656 40587583 41267525 41667463 42327297
               43237154 44267029 44996935 45146868 45206771 44556743
               43986920 42687064 41687044 41117238 40827345 39677454
               38997575 38987703