MESOSCALE DISCUSSION 1204
   NWS STORM PREDICTION CENTER NORMAN OK
   1040 AM CDT THU JUN 18 2009
   
   AREAS AFFECTED...SERN PA INTO NJ AND SWD THROUGH THE DELMARVA
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 181540Z - 181715Z
   
   THE THREAT FOR SEVERE STORMS INCLUDING SUPERCELLS CAPABLE OF
   HAIL...DAMAGING WINDS AND PERHAPS TORNADOES IS EXPECTED TO INCREASE
   THIS AFTERNOON.  CONVECTIVE TRENDS ARE BEING MONITORED FOR A
   POSSIBLE WW.
   
   LATEST MESOANALYSIS INDICATED A WEAK SURFACE LOW OVER CNTRL MD INTO
   S-CNTRL/SERN PA WHICH IS FORECAST TO DEVELOP SLOWLY EWD/SEWD THIS
   AFTERNOON PER 12Z MODEL GUIDANCE.  AS THIS OCCURS...ATTENDANT WARM
   FRONT EXTENDING FROM THE LOW SSEWD THROUGH CHESAPEAKE BAY SHOULD
   DEVELOP EWD/NEWD THROUGH PARTS OF ERN MD...DE AND PERHAPS SRN NJ.
   
   WARM SECTOR AIR MASS IN PLACE OVER CNTRL/ERN VA INTO CNTRL MD IS
   QUITE MOIST WITH DEWPOINTS IN THE UPPER 60S TO LOWER 70S.  WHEN
   COUPLED WITH THE AFTERNOON HEATING...AIR MASS WILL FURTHER
   DESTABILIZE WITH MLCAPE APPROACHING 1000-2000 J/KG.  AS
   SUCH...EXPECT CONVECTION CURRENTLY DEVELOPING FROM SERN PA THROUGH
   CNTRL MD INTO NRN VA TO INTENSIFY THIS AFTERNOON WITH ADDITIONAL
   TSTM DEVELOPMENT LIKELY INTO CNTRL/ERN VA ALONG SEWD-MOVING
   TROUGH/COLD FRONT.  
   
   CURRENT AREA VWPS INDICATE THE STRONGEST LOW-LEVEL SHEAR E OF WARM
   FRONT /REF. CURRENT DOX WIND PROFILE/ WITH NOTABLY WEAKER LOW-LEVEL
   WIND FIELDS WITHIN WARM SECTOR.  NONETHELESS...THE PRESENCE OF THE
   MODERATE INSTABILITY...30-40 KT OF DEEP LAYER SHEAR AND
   ISALLOBARICALLY BACKED SURFACE WINDS INVOF LOW AND WARM FRONT
   SUGGESTS THE POTENTIAL FOR A FEW SUPERCELLS CAPABLE OF
   HAIL...DAMAGING WINDS AND PERHAPS A FEW TORNADOES.
   
   ..MEAD.. 06/18/2009
   
   
   ATTN...WFO...PHI...AKQ...CTP...LWX...RNK...
   
   LAT...LON   37707829 39027762 40007706 40417636 40437556 40317493
               39537483 38467573 37467621 36997679 37107796 37707829