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WWUS20 KWNS 201721

SEL1

SPC WW 201721

INZ000-KYZ000-MDZ000-OHZ000-PAZ000-WVZ000-210100-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 621

NWS STORM PREDICTION CENTER NORMAN OK

120 PM EDT MON AUG 20 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHEAST INDIANA

       NORTH CENTRAL AND NORTHEAST KENTUCKY

       EXTREME WESTERN MARYLAND

       OHIO

       WESTERN PENNSYLVANIA

       NORTHERN  AND CENTRAL WEST VIRGINIA



EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 120 PM UNTIL 900

PM 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 70

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

SOUTHWEST OF DAYTON OHIO TO 30 MILES SOUTH SOUTHEAST OF LATROBE

PENNSYLVANIA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).



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...THUNDERSTORMS ARE EXPECTED TO CONTINUE DEVELOPING AND

INTENSIFY PRIMARILY ALONG/SOUTH OF EXISTING STORMS FROM NRN INDIANA

EWD ACROSS OH INTO WRN PA AND NRN WV.  THIS REGION IS RAPIDLY

WARMING AND DESTABILIZING AND VISIBLE IMAGERY SHOWS INCREASING

CU/TCU FIELD INDICATING CAP IS LIKELY WEAKENING.  DYNAMIC FORCING

ASSOCIATED WITH VORTICITY MAX MOVING ACROSS IL IS SPREADING

DOWNSTREAM INTO THE OH VALLEY.  30-40 KT LOW/MID LEVEL WINDS

EXHIBITED ON AREA VAD DISPLAYS WILL PROVIDE SUFFICIENT VERTICAL

SHEAR FOR SEVERE STORMS TO DEVELOP.



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 25030.





...WEISS

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