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204 

WWUS20 KWNS 300900

SEL8

SPC WW 300900

DCZ000-DEZ000-MDZ000-NCZ000-NJZ000-VAZ000-CWZ000-301700-



URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 688

NWS STORM PREDICTION CENTER NORMAN OK

455 AM EDT THU SEP 30 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       DISTRICT OF COLUMBIA

       DELAWARE

       EASTERN MARYLAND

       EASTERN NORTH CAROLINA

       SOUTHERN NEW JERSEY

       EASTERN VIRGINIA

       COASTAL WATERS



EFFECTIVE THIS THURSDAY MORNING AND AFTERNOON FROM 455 AM UNTIL

100 PM EDT.



TORNADOES...HAIL TO 0.5 INCH IN DIAMETER...THUNDERSTORM WIND

GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE

AREAS.



THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 60 STATUTE

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

DOVER DELAWARE TO 40 MILES SOUTH OF JACKSONVILLE NORTH CAROLINA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU8).



REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR

TORNADOES AND 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.



OTHER WATCH INFORMATION...THIS TORNADO WATCH REPLACES TORNADO

WATCH NUMBER 687. WATCH NUMBER 687 WILL NOT BE IN EFFECT AFTER

455 AM EDT.



DISCUSSION...A WELL-DEFINED LOW NEAR THE NC/SC BORDER WILL CONTINUE

NWD ACROSS CENTRAL NC/VA THROUGH THE MORNING.  A SLOW-MOVING FRONT

WILL ALSO MOVE INLAND SOME ACROSS VA IN ADVANCE OF THE

LOW...ALLOWING THE MOIST SECTOR WITH LOW 70S DEWPOINTS AND WEAK

SURFACE-BASED INSTABILITY TO LIKEWISE SPREAD INLAND.  EVEN THOUGH

THE LOW SHOULD WEAKEN GRADUALLY THROUGH THE MORNING...A BELT OF

60-70 KT LOW-LEVEL FLOW AND ENHANCED SRH WILL BE MAINTAINED ALONG

THE SLOW-MOVING FRONT.  THE STRONG SHEAR/WEAK INSTABILITY

ENVIRONMENT WILL SUPPORT SEVERAL BANDS WITH EMBEDDED SUPERCELLS AND

AN ATTENDANT RISK FOR A FEW TORNADOES...AS WELL AS ISOLATED

STRONG/DAMAGING GUSTS.  THE PRIMARY TORNADO THREAT EARLY THIS

MORNING WILL REMAIN ACROSS NC/SE VA...WITH THE THREAT EXPANDING NWD

DURING THE MORNING TOWARD THE DELMARVA...AND POTENTIALLY AS FAR NE

AS SRN NJ BY LATE MORNING.



AVIATION...TORNADOES AND 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

450. MEAN STORM MOTION VECTOR 18045.





...THOMPSON

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