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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 638

NWS STORM PREDICTION CENTER NORMAN OK

220 PM EDT WED JUL 13 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       DISTRICT OF COLUMBIA

       CENTRAL AND SOUTHERN DELAWARE

       CENTRAL AND SOUTHERN MARYLAND

       WESTERN AND NORTH CENTRAL NORTH CAROLINA

       VIRGINIA

       EXTREME EASTERN WEST VIRGINIA PANHANDLE

       COASTAL WATERS



EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 220 PM UNTIL

1000 PM EDT.



HAIL TO 1.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 90

STATUTE MILES EAST AND WEST OF A LINE FROM 10 MILES WEST

NORTHWEST OF BALTIMORE MARYLAND TO 30 MILES SOUTH OF GREENSBORO

NORTH CAROLINA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU8).



REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE

FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH

AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR

THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS

AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY

DO PRODUCE TORNADOES.



DISCUSSION...STORMS ARE DEVELOPING ALONG A SOUTHWARD MOVING COLD

FRONT FROM NRN WV ACROSS MD...WHILE ADDITIONAL STORMS HAVE DEVELOPED

JUST EAST OF THE MOUNTAINS INTO SWRN VA AND WRN NC.  AIR MASS IS

QUITE MOIST WITH SURFACE DEW POINTS IN THE LOW/MID 70S...AND

SUFFICIENT HEATING HAS OCCURRED TO DESTABILIZE THE ENVIRONMENT WITH

MLCAPE OF 1500-2000 J/KG.  WESTERLY FLOW ALOFT HAS STRENGTHENED

ALONG THE SRN EDGE OF A SHORT WAVE TROUGH MOVING INTO THE MID

ATLANTIC STATES...WITH 30-40 KT VAD WINDS EVIDENT FROM FCX AND LWX

RADARS.  THIS IS CREATING SUFFICIENT VERTICAL SHEAR TO ENHANCE STORM

ORGANIZATION.  DAMAGING WIND GUSTS WILL BE THE PRIMARY THREAT

ALTHOUGH ISOLATED LARGE HAIL WILL ALSO BE POSSIBLE.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 28025.





...WEISS

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