

000 

WWUS20 KWNS 292038

SEL3

SPC WW 292038

DCZ000-DEZ000-MDZ000-NJZ000-VAZ000-WVZ000-CWZ000-300400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 643

NWS STORM PREDICTION CENTER NORMAN OK

440 PM EDT SUN JUN 29 2008



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       DISTRICT OF COLUMBIA

       DELAWARE

       MARYLAND

       PARTS OF SOUTHERN NEW JERSEY

       MUCH OF VIRGINIA

       SMALL PART OF EASTERN WEST VIRGINIA

       COASTAL WATERS



EFFECTIVE THIS SUNDAY AFTERNOON FROM 440 PM UNTIL MIDNIGHT 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 120

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

NORTHWEST OF BALTIMORE MARYLAND TO 10 MILES SOUTHWEST OF SOUTH

HILL VIRGINIA.  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.



OTHER WATCH INFORMATION...CONTINUE...WW 637...WW 638...WW

639...WW 640...WW 641...WW 642...



DISCUSSION...THUNDERSTORMS ARE INCREASING ACROSS THE WARN PORTION OF

WATCH AREA AS AIR MASS CONTINUES TO DESTABILIZE AHEAD OF

UNSEASONABLY STRONG UPPER TROUGH.  40KT OF DEEP LAYER SHEAR AND

STEEP LOW LEVEL LAPSE RATES SUPPORT WIND DAMAGE AS STORMS EVOLVE

INTO LINE SEGMENTS AND MULTICELLULAR CLUSTERS.



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 500. MEAN STORM

MOTION VECTOR 24030.





...HALES

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