Post by Nws Olney Maryland on Jul 13, 2011 14:15:11 GMT -5
URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 638
NWS STORM PREDICTION CENTER OLNEY MD
220 PM EDT WED JUL 13 2011
THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
DISTRICT OF COLUMBIA
CENTRAL AND SOUTHERN DELAWARE
CENTRAL AND SOUTHERN MARYLAND
WESTERN AND NORTH CENTRAL NORTH CAROLINA
VIRGINIA
EXTREME EASTERN WEST VIRGINIA PANHANDLE
COASTAL WATERS
EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 220 PM UNTIL
1000 PM EDT.
SCATTERED DAMAGING WINDS TO 70 MPH
WIDELY SCATTERED LARGE HAIL TO 1.5 INCHES IN DIAMETER
THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 90
STATUTE MILES EAST AND WEST OF A LINE FROM 10 MILES WEST
NORTHWEST OF BALTIMORE MARYLAND TO 30 MILES SOUTH OF GREENSBORO
NORTH CAROLINA. 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.
DISCUSSION...STORMS ARE DEVELOPING ALONG A SOUTHWARD MOVING COLD
FRONT FROM NRN WV ACROSS MD...WHILE ADDITIONAL STORMS HAVE DEVELOPED
JUST EAST OF THE MOUNTAINS INTO SWRN VA AND WRN NC. AIR MASS IS
QUITE MOIST WITH SURFACE DEW POINTS IN THE LOW/MID 70S...AND
SUFFICIENT HEATING HAS OCCURRED TO DESTABILIZE THE ENVIRONMENT WITH
MLCAPE OF 1500-2000 J/KG. WESTERLY FLOW ALOFT HAS STRENGTHENED
ALONG THE SRN EDGE OF A SHORT WAVE TROUGH MOVING INTO THE MID
ATLANTIC STATES...WITH 30-40 KT VAD WINDS EVIDENT FROM FCX AND LWX
RADARS. THIS IS CREATING SUFFICIENT VERTICAL SHEAR TO ENHANCE STORM
ORGANIZATION. DAMAGING WIND GUSTS WILL BE THE PRIMARY THREAT
ALTHOUGH ISOLATED LARGE HAIL WILL ALSO BE POSSIBLE.
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 28025.