MESOSCALE DISCUSSION 1947
   NWS STORM PREDICTION CENTER NORMAN OK
   0221 PM CDT FRI AUG 21 2009
   
   AREAS AFFECTED...ERN VA...ERN MD...DEL
   
   CONCERNING...SEVERE THUNDERSTORM WATCH 728...
   
   VALID 211921Z - 212045Z
   
   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 728
   CONTINUES.
   
   THREAT FOR MAINLY ISOLATED DAMAGING WIND AND POSSIBLY MARGINALLY
   SEVERE HAIL WILL PERSIST NEXT FEW HOURS ACROSS ERN VA INTO ERN MD
   AND DEL.
   
   THE 18Z RAOBS FROM RNK...IAD AND WAL AS WELL AS RUC ANALYSIS
   INDICATED A RESERVOIR OF MODERATE INSTABILITY WITH THE GREATER
   INSTABILITY LOCATED OVER SERN VA...SOMEWHAT DISPLACED FROM THE
   STRONGER VERTICAL SHEAR FARTHER WEST. STORMS CURRENTLY DEVELOPING
   FROM ERN VA THROUGH ERN MD ARE EMBEDDED WITHIN MODEST /< 35 KT/ BULK
   SHEAR AND APPEAR ONLY LOOSELY ORGANIZED. THESE STORMS MAY REMAIN
   CAPABLE OF PRODUCING ISOLATED WIND DAMAGE. ADDITIONAL STORMS MAY YET
   DEVELOP FARTHER SOUTH ACROSS SERN VA WHERE TEMPERATURES HAVE WARMED
   TO NEAR 90 RESULTING IN 2500-3000 J/KG MLCAPE...BUT WHERE MODEST
   VERTICAL SHEAR WILL SUPPORT MULTICELL STORMS. PRIMARILY LIMITING
   FACTORS THUS FAR FOR A MORE ROBUST SEVERE THREAT HAS BEEN THE WARM
   AIR ALOFT WITH -4 TO -5C AT 500 MB ALONG WITH TENDENCY FOR THE
   STRONGER DEEP LAYER SHEAR TO REMAIN WEST OF THE MORE UNSTABLE WARM
   SECTOR.
   
   ..DIAL.. 08/21/2009
   
   
   ATTN...WFO...PHI...AKQ...LWX...RNK...
   
   LAT...LON   36917683 36697910 39077662 39427495 36917683