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WWUS20 KWNS 182029

SEL9

SPC WW 182029

NDZ000-SDZ000-190300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 659

NWS STORM PREDICTION CENTER NORMAN OK

230 PM MDT MON JUL 18 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHWEST NORTH DAKOTA

       NORTHWEST SOUTH DAKOTA



EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 230 PM UNTIL 900

PM MDT.



HAIL TO 2.5 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 65

STATUTE MILES EAST AND WEST OF A LINE FROM 60 MILES NORTH

NORTHWEST OF LEMMON SOUTH DAKOTA TO 100 MILES SOUTH SOUTHEAST OF

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

THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU9).



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 657...WW 658...



DISCUSSION...AN ISOLATED THUNDERSTORM HAS DEVELOPED OVER THE N SLOPE

OF THE BLACK HILLS...AND ADDITIONAL DEVELOPING STORMS ARE LOCATED

ALONG THE SURFACE WARM FRONT IN HARDING COUNTY SD.  CONTINUED

SURFACE HEATING WILL FURTHER ERODE THE CAP...WHILE STRONG

INSTABILITY IS PRESENT ALONG THE BOUNDARY.  THE COMBINATION OF

INSTABILITY AND VERTICAL SHEAR WILL SUPPORT SUPERCELLS CAPABLE OF

PRODUCING LARGE HAIL AND DAMAGING WINDS.  AN ISOLATED COULD ALSO

OCCUR RIGHT ALONG THE WARM FRONT...WHERE LOW-LEVEL SHEAR AND

MOISTURE WILL BE RELATIVELY GREATER.



AVIATION...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 600. MEAN STORM

MOTION VECTOR 25020.





...THOMPSON

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