

000 

WWUS20 KWNS 091351

SEL3

SPC WW 091351

DCZ000-MDZ000-PAZ000-VAZ000-WVZ000-CWZ000-092000-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 573

NWS STORM PREDICTION CENTER NORMAN OK

950 AM EDT THU AUG 9 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       DISTRICT OF COLUMBIA

       MARYLAND

       CENTRAL AND SOUTHEAST PENNSYLVANIA

       NORTHERN VIRGINIA

       EASTERN WEST VIRGINIA PANHANDLE

       COASTAL WATERS



EFFECTIVE THIS THURSDAY MORNING AND AFTERNOON FROM 950 AM UNTIL

400 PM EDT.



HAIL TO 2 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 60

STATUTE MILES EITHER SIDE OF A LINE FROM 30 MILES WEST OF ALTOONA

PENNSYLVANIA TO 40 MILES NORTHEAST OF BALTIMORE MARYLAND.  FOR A

COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE

UPDATE (WOUS64 KWNS WOU3).



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...LINE OF STRONG/SEVERE THUNDERSTORMS HAS DEVELOPED OVER

SWRN PA.  THIS IS EXPECTED TO MOVE EWD/ESEWD AS NEW DEVELOPMENT

OCCURS ON THE SRN END OF THE LINE.  12Z SOUNDINGS AT IAD AND WAL

INDICATE LITTLE REMAINING CAP AS LOW LEVEL AIR MASS RAPIDLY WARMS

WITH SURFACE TEMPERATURES ALREADY AROUND 90F.  MID LEVEL FLOW OF

30-40 KT INDICATED ON PBZ VAD PROFILE SHOULD MAINTAIN FORWARD

PROPAGATION OF CONVECTIVE SYSTEM AS IT MOVES INTO VERY MOIST AND

MODERATELY UNSTABLE ENVIRONMENT.



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

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM

MOTION VECTOR 27020.





...WEISS

