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630 

WWUS20 KWNS 251923

SEL7

SPC WW 251923

DCZ000-MDZ000-VAZ000-CWZ000-260100-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 807

NWS STORM PREDICTION CENTER NORMAN OK

325 PM EDT THU AUG 25 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       DISTRICT OF COLUMBIA

       LOWER MARYLAND

       CENTRAL AND NORTHERN VIRGINIA

       COASTAL WATERS



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 325 PM UNTIL

900 PM EDT.



HAIL TO 1 INCH 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 40

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 40 MILES WEST OF

LYNCHBURG VIRGINIA TO 45 MILES EAST OF PATUXENT RIVER MARYLAND.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU7).



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...SCATTERED THUNDERSTORMS WILL CONTINUE TO FORM IN A

BROKEN BAND ALONG A DIFFERENTIAL HEATING BOUNDARY ACROSS NRN VA...IN

ADVANCE OF A MIDLEVEL TROUGH EJECTING EWD FROM WV.  A NARROW ZONE OF

MODERATE INSTABILITY OVERLAPS THE SRN FRINGE OF THE STRONGER

MIDLEVEL FLOW...WHERE ORGANIZED MULTICELL CLUSTERS WILL BE CAPABLE

OF PRODUCING ISOLATED DAMAGING GUSTS AND MARGINALLY SEVERE HAIL FOR

THE NEXT FEW HOURS.



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

TO 1 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60 KNOTS.

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

VECTOR 27025.





...THOMPSON

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