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640 

WWUS20 KWNS 171434

SEL2

SPC WW 171434

DCZ000-MDZ000-NCZ000-VAZ000-WVZ000-CWZ000-172100-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 592

NWS STORM PREDICTION CENTER NORMAN OK

1030 AM EDT FRI JUL 17 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       DISTRICT OF COLUMBIA

       EASTERN MARYLAND

       NORTH CENTRAL NORTH CAROLINA

       CENTRAL AND PARTS OF EASTERN VIRGINIA

       FAR EASTERN WEST VIRGINIA

       COASTAL WATERS



EFFECTIVE THIS FRIDAY MORNING AND AFTERNOON FROM 1030 AM UNTIL

500 PM EDT.



HAIL TO 1.5 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 60

STATUTE MILES EAST AND WEST OF A LINE FROM 25 MILES NORTH

NORTHWEST OF BALTIMORE MARYLAND TO 35 MILES EAST SOUTHEAST OF

GREENSBORO NORTH CAROLINA.  FOR A COMPLETE DEPICTION OF THE WATCH

SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).



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...TSTMS DEVELOPING OVER THE BLUE RIDGE SHOULD INCREASE IN

COVERAGE AND INTENSITY TODAY WHILE PROGRESSING EWD INTO THE PIEDMONT

AND EVENTUALLY COASTAL PLAINS.  INFLOW AIR MASS IS MOIST...AND WHEN

COUPLED WITH MODEST DIABATIC HEATING AND STEEP MIDLEVEL LAPSE

RATES...ENVIRONMENT WILL BECOME MODERATELY UNSTABLE BY AFTERNOON

WITH MLCAPE OF AT LEAST 1000-1500 J/KG.  REGIONAL VWPS INDICATE A

NOTABLE INCREASE IN MID/HIGH-LEVEL FLOW IN CONJUNCTION WITH SHORT

WAVE TROUGH CURRENTLY MOVING THROUGH THE CUMBERLAND PLATEAU.  THIS

STRENGTHENING VERTICAL SHEAR IN CONCERT WITH THE MODERATE

INSTABILITY SHOULD FOSTER ORGANIZED LINE SEGMENTS AND PERHAPS

SUPERCELL STRUCTURES WITH THE PRIMARY SEVERE THREATS BEING DAMAGING

WINDS AND HAIL.



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

TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 27035.





...MEAD/IMY

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