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WWUS20 KWNS 171458

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SPC WW 171458

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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 650

NWS STORM PREDICTION CENTER NORMAN OK

955 AM CDT SUN JUL 17 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHWEST MINNESOTA

       NORTHERN AND EASTERN NORTH DAKOTA



EFFECTIVE THIS SUNDAY MORNING AND AFTERNOON FROM 955 AM UNTIL 500

PM CDT.



HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 80

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



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 65

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 90 MILES WEST OF

DEVILS LAKE NORTH DAKOTA TO 20 MILES NORTHEAST OF BEMIDJI

MINNESOTA.  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.



DISCUSSION...A PERSISTENT CLUSTER OF TSTMS NEAR MINOT HAS SHOWN

SIGNS OF INTENSIFICATION IN THE PAST 30 MINUTES.  THOUGH CONVECTIVE

INHIBITION STILL REMAINS SUBSTANTIAL FOR SURFACE-BASED PARCELS...THE

DOWNSTREAM ENVIRONMENT IS EXTREMELY UNSTABLE ACROSS ND...AND MLCAPE

WILL LIKELY EXCEED 6000 J/KG WITH ADDITIONAL DAYTIME HEATING BY

EARLY-MID AFTERNOON.  MEANWHILE...A WELL-DEFINED SPEED MAX IS

CRESTED THE RIDGE FROM NE MT INTO NW ND...AND ASCENT IN ADVANCE OF

THIS WAVE WILL HELP SUPPORT UPSCALE GROWTH OF THE STORM CLUSTER AS

IT MOVES EWD ALONG A RESIDUAL SURFACE BOUNDARY INTO E/NE ND.

VERTICAL SHEAR AND INSTABILITY WILL SUPPORT BOTH SUPERCELLS AND BOW

ECHOES WITH THE POTENTIAL FOR VERY LARGE HAIL AND DAMAGING GUSTS.

AN ISOLATED TORNADO CANNOT BE RULED OUT...ESPECIALLY BY AFTERNOON AS

THE BOUNDARY LAYER WARMS/DESTABILIZES.  OTHERWISE...THE STORMS COULD

GROW UPSCALE INTO A BOWING MCS...WITH THE POTENTIAL FOR MORE

WIDESPREAD AND SIGNIFICANT WIND DAMAGE THIS AFTERNOON.



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

TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 70

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 650. MEAN STORM

MOTION VECTOR 28035.





...THOMPSON

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