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000 

WWUS20 KWNS 200239

SEL0

SPC WW 200239

SDZ000-201000-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 620

NWS STORM PREDICTION CENTER NORMAN OK

840 PM MDT SUN AUG 19 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WESTERN AND SOUTHERN SOUTH DAKOTA



EFFECTIVE THIS SUNDAY NIGHT AND MONDAY MORNING FROM 840 PM UNTIL

400 AM MDT.



HAIL TO 1.5 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 90

STATUTE MILES EAST AND WEST OF A LINE FROM 70 MILES EAST

NORTHEAST OF BUFFALO SOUTH DAKOTA TO 75 MILES SOUTH SOUTHWEST OF

PHILIP SOUTH DAKOTA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE

THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU0).



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 618...WW 619...



DISCUSSION...TSTMS OVER ERN WY EXPECTED TO CONTINUE E INTO WRN/SRN

SD LATER TONIGHT AND EARLY MONDAY AS LEADING EDGE OF HEIGHT

FALLS/INCREASED WLY FLOW OVERSPREAD REGION DOWNSTREAM FROM NRN RCKYS

UPR IMPULSE.  MODERATELY MOIST ESELY LOW LVL FLOW AND LOW LVL

VEERING PROFILES SUGGEST POTENTIAL FOR SUPERCELL STRUCTURES WITH A

THREAT FOR HAIL/HIGH WIND AND POSSIBLY A TORNADO.  WITH

STRENGTHENING SSWLY LLJ IMPINGING ON WNW/ESE-ORIENTED THERMAL

GRADIENT...ACTIVITY SHOULD MERGE INTO AN MCS THAT MOVES E/ESE INTO

CNTRL/SRN SD EARLY MONDAY.



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 26030.





...CORFIDI

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