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954 

WWUS20 KWNS 250453

SEL7

SPC WW 250453

IAZ000-NEZ000-SDZ000-251000-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 507

NWS STORM PREDICTION CENTER NORMAN OK

1155 PM CDT WED JUN 24 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       PARTS OF NORTHWEST IOWA

       NORTHEASTERN NEBRASKA

       PARTS OF SOUTHEASTERN SOUTH DAKOTA



EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 1155 PM

UNTIL 500 AM CDT.



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 90

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 35 MILES WEST

SOUTHWEST OF ONEILL NEBRASKA TO 30 MILES EAST OF SIOUX CITY IOWA.

 FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU7).



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...THIS SEVERE THUNDERSTORM WATCH REPLACES

SEVERE THUNDERSTORM WATCH NUMBER 506. WATCH NUMBER 506 WILL NOT

BE IN EFFECT AFTER 1155 PM CDT.



DISCUSSION...PERSISTENT SUPERCELLS CONTINUE TO DEVELOP S/SEWD INTO A

VERY MOIST AND UNSTABLE AIR MASS.  DEEP LAYER SHEAR OF 40KT SUPPORTS

THE SUPERCELLS MAINTAINING THE POTENTIAL FOR DAMAGING WINDS/LARGE

HAIL AND BRIEF TORNADOES THE NEXT FEW HOURS.



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 550. MEAN STORM

MOTION VECTOR 34025.





...HALES

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