MESOSCALE DISCUSSION 1943
   NWS STORM PREDICTION CENTER NORMAN OK
   0251 PM CDT MON JUL 21 2003
   
   AREAS AFFECTED...PA...SRN NY
   
   CONCERNING...SEVERE THUNDERSTORM WATCH 787...
   
   VALID 211951Z - 212145Z
   
   INTENSE CONVECTIVELY-GENERATED MESOSCALE VORTICITY MAXIMA IS
   WELL-DEFINED IN RADAR IMAGERY OVER NWRN PA MOVING ENEWD 45 KT. 
   LINEAR EXTRAPOLATION OF THIS FEATURE PLACES IT INTO SOUTH CENTRAL NY
   BETWEEN 21-22Z.  A SMALL-SCALE COMMA CLOUD OF CONVECTION IS
   GRADUALLY DEVELOPING SWD THROUGH CENTRAL PA IN ADVANCE OF THE MCV AS
   IT MOVES THROUGH UNSTABLE AIR MASS WITH SBCAPE OF 1500-2500 J/KG. 
   VAD PROFILES CONTINUE TO SHOW STRONG WSWLY WINDS OF 40-50 KT ABOVE
   700 MB PROVIDING DEEP LAYER VERTICAL SHEAR OF 35-45 KT...SUPPORTIVE
   OF SEVERE THUNDERSTORM ACTIVITY.  PRIMARY THREAT WILL BE FOR
   DAMAGING WIND GUSTS AS STORMS MOVE ENEWD 40-45 KT.  IN
   ADDITION...STRONG LOW LEVEL SHEAR/HELICITY AND LOW LCL HEIGHTS
   INDICATE THREAT FOR AN ISOLATED TORNADO OR TWO...ESPECIALLY OVER
   NORTH CENTRAL PA WHERE CONVECTIVE LINE INTERSECTS WARM FRONT.
   
   ..WEISS.. 07/21/2003
   
   
   ATTN...WFO...PHI...BGM...BUF...CTP...PBZ...
   
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