

140 

WWUS20 KWNS 220008

SEL0

SPC WW 220008

OKZ000-220500-



URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 320

NWS STORM PREDICTION CENTER NORMAN OK

710 PM CDT SAT MAY 21 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       PARTS OF SOUTH CENTRAL AND SOUTHEAST OKLAHOMA



EFFECTIVE THIS SATURDAY NIGHT FROM 710 PM UNTIL MIDNIGHT CDT.



TORNADOES...HAIL TO 3 INCHES IN DIAMETER...THUNDERSTORM WIND

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

AREAS.



THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 55 STATUTE

MILES EAST AND WEST OF A LINE FROM 45 MILES NORTH NORTHWEST OF

MCALESTER OKLAHOMA TO 15 MILES SOUTHWEST OF DURANT OKLAHOMA.  FOR

A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU0).



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...CONTINUE...WW 316...WW 317...WW

318...WW 319...



DISCUSSION...AN ISOLATED STORM FORMED EARLIER ON THE DRYLINE IN S

CENTRAL OK...WHILE VISIBLE IMAGERY NOW SHOWS MORE DEEPENING

CONVECTION FARTHER TO THE N.  EVEN THOUGH THE BOUNDARY LAYER HAS

REMAINED RELATIVELY COOL FARTHER TO THE E ACROSS SE OK TODAY...THE

COMBINATION OF STEEP MIDLEVEL LAPSE RATES AND DEWPOINTS NEAR 70 F

WILL MAINTAIN MLCAPE AOA 2500 J/KG FOR THE NEXT SEVERAL HOURS.

SINCE IT APPEARS THAT ONE OR TWO STORMS WILL BECOME SUSTAINED...THE

ENVIRONMENT IS SUPPORTIVE OF SUPERCELLS WITH VERY LARGE HAIL AND A

COUPLE OF TORNADOES.



AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL

SURFACE AND ALOFT TO 3 INCHES. EXTREME TURBULENCE AND SURFACE

WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO

550. MEAN STORM MOTION VECTOR 27025.





...THOMPSON

