WATCHES: Severe Thunderstorm Watch Number 673

WWUS20 KWNS 072255
SEL3
SPC WW 072255
SDZ000-080500-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 673
NWS STORM PREDICTION CENTER NORMAN OK
455 PM MDT FRI AUG 7 2009

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

WESTERN SOUTH DAKOTA

EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 455 PM UNTIL
1100 PM MDT.

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 60
STATUTE MILES EAST AND WEST OF A LINE FROM 40 MILES NORTHEAST OF
BUFFALO SOUTH DAKOTA TO 75 MILES SOUTH SOUTHEAST OF RAPID CITY
SOUTH DAKOTA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU3).

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.

OTHER WATCH INFORMATION...CONTINUE...WW 672...

DISCUSSION...THUNDERSTORMS WILL CONTINUE DEVELOPING ENEWD ACROSS WRN
SD THROUGH THE EVENING AHEAD OF LARGE UPPER LOW OVER THE NRN
ROCKIES. REGION REMAINS WITHIN NLY SFC FLOW IN WAKE OF A SURFACE
COLD FRONT...HOWEVER SUFFICIENT INSTABILITY REMAINS FOR ROBUST
THUNDERSTORM DEVELOPMENT...DESPITE BECOMING SOMEWHAT ELEVATED.
SHEAR WILL ALSO REMAIN SUPPORTIVE OF SUPERCELLS...WITH SPLITTING
STORMS LIKELY GIVEN LARGE STRAIGHT HODOGRAPHS. MOST LIKELY AREA
WILL BE INTO NWRN SD THIS EVENING...ALTHOUGH DEEP MIXING MAY ALSO
SUPPORT ISOLATED SEVERE THUNDERSTORMS NEAR THE NEB BORDER.

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 450. MEAN STORM
MOTION VECTOR 23030.

...EVANS

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