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WWUS20 KWNS 251721

SEL9

SPC WW 251721

DCZ000-DEZ000-MDZ000-NJZ000-PAZ000-VAZ000-CWZ000-252100-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 19

NWS STORM PREDICTION CENTER NORMAN OK

1220 PM EST FRI FEB 25 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       DISTRICT OF COLUMBIA

       DELAWARE

       THE EASTERN SHORE OF MARYLAND

       SOUTHERN NEW JERSEY

       EXTREME SOUTHEAST PENNSYLVANIA

       NORTHEAST VIRGINIA

       COASTAL WATERS



EFFECTIVE THIS FRIDAY AFTERNOON FROM 1220 PM UNTIL 400 PM EST.



HAIL TO 0.5 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 65

STATUTE MILES EAST AND WEST OF A LINE FROM PHILADELPHIA

PENNSYLVANIA TO 5 MILES WEST SOUTHWEST OF PATUXENT RIVER

MARYLAND.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU9).



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...LOW-TOPPED CONVECTION IS GRADUALLY INCREASING WITHIN

THE MIDLEVEL DRY SLOT...JUST IN ADVANCE OF AN EJECTING MIDLEVEL

TROUGH AND A SURFACE COLD FRONT.  SURFACE HEATING IN THE DRY SLOT

AND RESIDUAL BOUNDARY LAYER DEWPOINTS IN THE MID 50S WILL SUPPORT

SBCAPE NEAR 500 J/KG...WHILE STRONG WINDS JUST ABOVE THE SURFACE

WILL FAVOR MOMENTUM TRANSFER TO THE GROUND AND DAMAGING WIND

POTENTIAL WITH THE STRONGER LINE SEGMENTS/CELLS.  ADDITIONALLY...THE

STRONG LOW-LEVEL SHEAR COULD SUPPORT ROTATING STORMS...AND AN

ISOLATED TORNADO CANNOT BE RULED OUT THIS AFTERNOON.



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

TO 0.5 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 300. MEAN STORM

MOTION VECTOR 27045.





...THOMPSON

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