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815 

WWUS20 KWNS 081617

SEL6

SPC WW 081617

DCZ000-DEZ000-MDZ000-NJZ000-PAZ000-VAZ000-WVZ000-CWZ000-090200-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 636

NWS STORM PREDICTION CENTER NORMAN OK

1215 PM EDT SAT SEP 8 2012



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       DISTRICT OF COLUMBIA

       DELAWARE

       MUCH OF MARYLAND

       NEW JERSEY

       EASTERN PENNSYLVANIA

       NORTHERN VIRGINIA

       THE EASTERN PANHANDLE OF WEST VIRGINIA

       COASTAL WATERS



EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 1215 PM UNTIL

1000 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 100

STATUTE MILES EAST AND WEST OF A LINE FROM 50 MILES NORTH

NORTHWEST OF ALLENTOWN PENNSYLVANIA TO 55 MILES SOUTHWEST OF

WASHINGTON DISTRICT OF COLUM.  FOR A COMPLETE DEPICTION OF THE

WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU6).



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.



OTHER WATCH INFORMATION...CONTINUE...WW 634...WW 635...



DISCUSSION...FRONTAL SQUALL LINE IS EXPECTED TO INTENSIFY THIS

AFTERNOON AS IT ENCOUNTERS THE AREA OF GREATER SURFACE

HEATING/INSTABILITY ACROSS ERN PA/MD/VA.  INCREASING LOW-MIDLEVEL

FLOW WITH AN EJECTING SHORTWAVE TROUGH WILL LIKEWISE CONTRIBUTE TO

AN INCREASING RISK FOR WIDESPREAD DAMAGING WINDS THIS AFTERNOON THIS

AFTERNOON/EVENING.



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 450. MEAN STORM MOTION

VECTOR 26040.





...THOMPSON

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