MESOSCALE DISCUSSION 2030
   NWS STORM PREDICTION CENTER NORMAN OK
   1054 AM CDT SUN AUG 21 2011
   
   AREAS AFFECTED...PARTS OF NRN VA...THE DELMARVA...SRN AND ERN
   PA...NJ...INTO THE LWR HUDSON VALLEY
   
   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 
   
   VALID 211554Z - 211800Z
   
   TRENDS ARE BEING MONITORED FOR AN INCREASING SEVERE THREAT THAT
   COULD REQUIRE ONE OR MORE WATCHES DURING THE 17-19Z TIME FRAME.
   
   BENEATH DIFLUENT UPPER FLOW DOWNSTREAM OF A VIGOROUS SHORT WAVE
   TROUGH NOW TURNING EASTWARD THROUGH THE GREAT LAKES REGION...
   SCATTERED THUNDERSTORM ACTIVITY IS ONGOING THROUGH MUCH OF THE
   NORTHEAST.  ASSOCIATED CLOUD COVER AND PRECIPITATION ARE SLOWING
   BOUNDARY LAYER DESTABILIZATION IN BROAD POCKETS...COMPLICATING THE
   SEVERE WEATHER POTENTIAL...WITH SOUTHWESTERLY DEEP LAYER MEAN FLOW
   AND SHEAR STILL SOMEWHAT MODEST ACROSS MUCH OF THE REGION.
   
   IT DOES APPEAR ONE AREA OF FORCING FOR ASCENT ASSOCIATED WITH A
   SMALLER SCALE IMPULSE/WEAK AREA OF MID-LEVEL HEIGHT FALLS IS
   BEGINNING TO SHIFT EAST NORTHEAST OF THE CENTRAL APPALACHIANS.  THIS
   COULD SUPPORT INCREASING STORM DEVELOPMENT WITHIN THE NEXT FEW HOURS
   ACROSS NORTHERN VIRGINIA INTO PARTS OF SOUTH CENTRAL/ SOUTHEAST
   PENNSYLVANIA...WHERE STRONGEST SURFACE HEATING IS OCCURRING.  LATEST
   RUC GUIDANCE SUGGESTS INHIBITION FOR MOIST BOUNDARY LAYER PARCELS
   CHARACTERIZED BY 70F+ SURFACE DEW POINTS IS DIMINISHING...AND MIXED
   LAYER CAPE COULD EXCEED 2000 J/KG TOWARD THE 18-20Z.
   
   THEREAFTER...THE SEVERE WEATHER POTENTIAL...INCLUDING THE RISK FOR
   ISOLATED SUPERCELLS AND ORGANIZED STORM CLUSTERS...APPEARS LIKELY TO
   GRADUALLY INCREASE THROUGH THE REMAINDER OF THE AFTERNOON.  THIS
   PROBABLY WILL INCLUDE AREAS FROM THE LEE OF THE LOWER GREAT LAKES
   EASTWARD INTO NEW ENGLAND...BUT IT REMAINS UNCLEAR WHETHER THE
   THREAT WILL BECOME WIDESPREAD...OR REMAIN RELATIVELY LOCALIZED
   ACROSS THESE AREAS.
   
   ..KERR.. 08/21/2011
   
   
   ATTN...WFO...BOX...OKX...ALY...PHI...BGM...AKQ...CTP...LWX...
   
   LAT...LON   39757874 40387831 40777707 41447561 42287465 42777388
               42557270 41517263 40507351 39467449 38727508 38127572
               37707697 37817765 38387860 39077833 39417880 39757874