

712 

WWUS20 KWNS 211645

SEL8

SPC WW 211645

DCZ000-DEZ000-MDZ000-NJZ000-VAZ000-CWZ000-220100-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 728

NWS STORM PREDICTION CENTER NORMAN OK

1235 PM EDT FRI AUG 21 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       DISTRICT OF COLUMBIA

       DELAWARE

       MARYLAND

       SOUTHERN NEW JERSEY

       CENTRAL AND EASTERN VIRGINIA

       COASTAL WATERS



EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 1235 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 75

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

NORTHWEST OF DOVER DELAWARE TO 25 MILES WEST SOUTHWEST OF SOUTH

HILL VIRGINIA.  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.



OTHER WATCH INFORMATION...CONTINUE...WW 726...WW 727...



DISCUSSION...THUNDERSTORMS ARE DEVELOPING ALONG THE ERN SLOPES OF

THE APPALACHIANS AND WILL SHIFT EWD THROUGH THE AFTERNOON. THE AIR

MASS IS EXTREMELY MOIST...DEWPOINTS IN THE MID/UPPER 70S...AND

TEMPERATURES IN THE 90S ARE RESULTING IN MODERATE TO STRONG

INSTABILITY. STRENGTHENING WINDS ALOFT AND 30-40 KT DEEP LAYER SHEAR

WILL BE FAVORABLE FOR THUNDERSTORM LINES AND PERHAPS EVEN SOME

SUPERCELL STRUCTURES...WITH WIND DAMAGE THE PRIMARY THREAT.



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 24025.





...IMY

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