

000 

WWUS20 KWNS 162357

SEL2

SPC WW 162357

SDZ000-170800-



URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 402

NWS STORM PREDICTION CENTER NORMAN OK

555 PM MDT SAT JUN 16 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       WESTERN SOUTH DAKOTA



EFFECTIVE THIS SATURDAY AFTERNOON AND SUNDAY MORNING FROM 555 PM

UNTIL 200 AM MDT.



TORNADOES...HAIL TO 2.5 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 60 STATUTE

MILES EAST AND WEST OF A LINE FROM 35 MILES NORTHEAST OF BUFFALO

SOUTH DAKOTA TO 40 MILES SOUTH SOUTHEAST OF RAPID CITY SOUTH

DAKOTA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED

WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).



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 400...WW 401...



DISCUSSION...THUNDERSTORMS WILL SPREAD EWD FROM NE WY INTO WRN SD

THE NEXT FEW HOURS...AND ADDITIONAL DEVELOPMENT WILL BE POSSIBLE

ALONG A BOUNDARY MOVING SLOWLY NWD ACROSS SW SD.  THE CAP HAS BEEN

WEAKENING GRADUALLY WITH WARMING SURFACE TEMPERATURES...AND BOUNDARY

LAYER DEWPOINTS HAVE NOW INCREASED INTO THE LOW-MID 60S ACROSS WRN

SD.  THE COMBINATION OF MLCAPE VALUES OF 2000-3000 J/KG...EFFECTIVE

BULK SHEAR NEAR 50 KT...AND EFFECTIVE SRH NEAR 300 M2/S2 WILL

SUPPORT SUPERCELLS CAPABLE OF PRODUCING TORNADOES...LARGE HAIL...AND

DAMAGING WINDS INTO TONIGHT.



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

SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE

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

500. MEAN STORM MOTION VECTOR 27030.





...THOMPSON

