ZCZC SPCSWOMCD ALL ACUS11 KWNS 211600 SPC MCD 211600 NJZ000-PAZ000-DEZ000-MDZ000-DCZ000-VAZ000-WVZ000-211730- MESOSCALE DISCUSSION 1002 NWS STORM PREDICTION CENTER NORMAN OK 1100 AM CDT TUE JUN 21 2016 AREAS AFFECTED...PARTS OF SRN PENNSYLVANIA/NEW JERSEY...MARYLAND/DELAWARE AND NRN VIRGINIA CONCERNING...SEVERE POTENTIAL...WATCH LIKELY VALID 211600Z - 211730Z PROBABILITY OF WATCH ISSUANCE...80 PERCENT SUMMARY...INCREASING AND INTENSIFYING THUNDERSTORM ACTIVITY IS EXPECTED ACROSS THE REGION...INCLUDING THE WASHINGTON D.C./BALTIMORE METRO AREAS...BY MID AFTERNOON. A SEVERE WEATHER WATCH IS LIKELY WITHIN THE NEXT HOUR OR TWO. DISCUSSION...THUNDERSTORMS HAVE INITIATED ALONG THE EASTERN SLOPES OF THE ALLEGHENY MOUNTAINS...NEAR A SURFACE FRONT ACROSS SOUTHERN PENNSYLVANIA...SOUTHWARD INTO PARTS OF NORTHWESTERN VIRGINIA. A DIVERGENT UPPER FLOW FIELD ON THE SOUTHERN PERIPHERY OF A BROAD CLOSED LOW CENTERED NEAR HUDSON BAY APPEARS TO BE SUPPORTING ACTIVITY...WHICH IS EXPECTED TO GRADUALLY INCREASE WHILE PROPAGATING OFF THE HIGHER TERRAIN BETWEEN NOW AND 17-19Z. A MOIST BOUNDARY LAYER /CHARACTERIZED BY SURFACE DEW POINTS OF 70F+/ ACROSS MUCH OF NORTHERN VIRGINIA INTO NORTHERN MID ATLANTIC COASTAL AREAS IS DESTABILIZING WITH INSOLATION...WITH MIXED LAYER CAPE ALREADY ESTIMATED ON THE ORDER OF 1500-2000 J/KG AND LOCALLY HIGHER. ALTHOUGH LOW/MID-LEVEL THERMAL LAPSE RATES ARE NOT PARTICULARLY STEEP...SEASONABLY HIGH MOISTURE CONTENT PROBABLY WILL BECOME INCREASING CONDUCIVE TO POTENTIAL FOR WET DOWNBURSTS WITH FURTHER BOUNDARY LAYER HEATING THIS AFTERNOON. BENEATH 40-50 KT WEST NORTHWESTERLY 500 MB FLOW...VERTICAL SHEAR APPEARS MORE THAN SUFFICIENT FOR ORGANIZED CONVECTION. THIS MAY INCLUDE ISOLATED SUPERCELLS...WITH AT LEAST SOME POTENTIAL FOR SEVERE HAIL. THE EVOLUTION OF AN UPSCALE GROWING MESOSCALE CONVECTIVE SYSTEM SEEMS POSSIBLE...WHICH COULD BE ACCOMPANIED BY BROADER-SCALE DAMAGING WIND GUST POTENTIAL ACROSS THE CHESAPEAKE/DELMARVA PENINSULA AREA BY LATE AFTERNOON. ..KERR/GUYER.. 06/21/2016 ...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT... ATTN...WFO...PHI...AKQ...CTP...LWX... LAT...LON 40267803 40217689 40107573 39687462 38947498 38447598 38547712 38577828 39107873 39947852 40267803 NNNN