SEVERE THUNDERSTORM WATCH UNTIL 10PM...EYE TO THE SKY for threatening weather.  Scattered thunderstorms through this evening.  Conditions have become favorable for the possibility of severe thunderstorms .  Some of the storms may contain damaging winds in excess of 58mph, torrential flooding rains, large hail and frequent cloud to ground lightning.  THUNDER ROARS GO INDOORS.

MESOSCALE DISCUSSION 1630 (12:30PM edt) NWS STORM PREDICTION CENTER NORMAN OK 1126 AM CDT SAT JUL 28 2012

AREAS AFFECTED...PORTIONS ERN PA...NRN/ERN VA...SWRN NEW ENGLAND...DE...SERN NY...DC..NJ...MD EXCEPT PANHANDLE. CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE VALID 281626Z - 281830Z PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...CONVECTION FCST TO INCREASE CONSIDERABLY IN COVERAGE ACROSS DISCUSSION AREA THROUGH MID-AFTN. MOST INTENSE CELLS WILL PRODUCE DAMAGING GUSTS AND OCNL HAIL. SEVERAL MULTICELLULAR CLUSTERS/BANDS WITH AGGREGATE COLD POOLS ALSO ARE POSSIBLE...ENHANCING WIND-DAMAGE POTENTIAL ON MESO-BETA SCALE. DISCUSSION...16Z SFC MESOANALYSIS SHOWED WAVY/QUASISTATIONARY FRONT FROM OFFSHORE LONG ISLAND WWD THROUGH WEAK LOW JUST OFF NRN NJ SHORE...THEN GENERALLY WWD OVER SRN PA AND SWWD FROM SWRN PA OVER OH VALLEY. SFC TROUGHS EXTENDED NWD FROM LOW NEAR HUDSON VALLEY AND SWWD FROM NRN NJ ACROSS CENTRAL CHESAPEAKE BAY TO S-CENTRAL VA AND WEAK LOW OVER WRN NC. EACH OF THOSE MAY FOCUS CONVECTIVE THREAT. RR MODEL REASONABLY INDICATES POTENTIAL FOR LOW TO FORM ALONG SRN TROUGH OVER CENTRAL/NRN VA...AS MID-UPPER LEVEL PERTURBATION APCHS. THIS WOULD FURTHER ENHANCE LOW-LEVEL CONVERGENCE/LIFT IN THAT AREA...AS WILL SEA-BREEZE AND BAY-BREEZE BOUNDARIES NEAR COASTLINES. AIR MASS ACROSS THIS REGION WILL CONTINUE FAVORABLE DESTABILIZATION...WITH STG SFC DIABATIC HEATING WELL UNDERWAY AND CINH NEARLY GONE OVER MOST OF AREA. INSOLATION AND PRESENCE OF RICH BOUNDARY-LAYER MOISTURE...EVIDENT IN SFC DEW POINTS LOW-MID 70S F AND 1.5-1.75 INCH GPS PW READINGS...WILL OFFSET WEAK LAPSE RATES ALOFT ENOUGH TO YIELD MLCAPE 1000-1500 J/KG.

VIS IMAGERY ACCORDINGLY SHOWS DEEP CU...TCU AND CB IN PATCHES FROM SRN PA AND NJ SWWD ACROSS CENTRAL/SRN MD AND ALSO DELMARVA PENINSULA...ON BOTH SIDES OF CHESAPEAKE BAY AND INVOF TROUGH. SWLY EFFECTIVE SHEAR VECTORS WITH 30-40 KT MAGNITUDES WILL AID IN MULTICELL ORGANIZATION...AND TRANSIENT SUPERCELL STRUCTURES CANNOT BE RULED OUT.