

149 

WWUS20 KWNS 182146

SEL6

SPC WW 182146

NDZ000-SDZ000-190400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 786

NWS STORM PREDICTION CENTER NORMAN OK

345 PM MDT THU AUG 18 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTH CENTRAL NORTH DAKOTA

       SOUTH DAKOTA



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 345 PM UNTIL

1000 PM MDT.



HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 75

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 95

STATUTE MILES EAST AND WEST OF A LINE FROM 55 MILES NORTH

NORTHEAST OF MOBRIDGE SOUTH DAKOTA TO 65 MILES SOUTH SOUTHEAST OF

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

THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU6).



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 785...



DISCUSSION...STORMS ARE GRADUALLY INCREASING OVER WRN SD ALONG/AHEAD

OF AN ADVANCING COLD FRONT...WITHIN AN ENVIRONMENT CHARACTERIZED BY

STRONG DEEP LAYER SHEAR AND INCREASING MOISTURE/INSTABILITY WITH EWD

EXTENT.  STORMS /INCLUDING A FEW SUPERCELLS/ ARE EXPECTED TO

INTENSIFY THROUGH THE EVENING HOURS WITH POTENTIAL FOR UPSCALE

GROWTH INTO A QLCS AS STRONG CONVECTIVE OUTFLOWS MERGE OVER THE NEXT

SEVERAL HOURS.  DAMAGING WIND GUSTS AND LARGE HAIL WILL BE THE

PRIMARY THREATS.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 65

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 27025.





...WEISS

