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WWUS20 KWNS 050434

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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 259

NWS STORM PREDICTION CENTER NORMAN OK

1135 PM CDT FRI JUN 4 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHWEST AND SOUTH CENTRAL IOWA

       EAST CENTRAL NEBRASKA



EFFECTIVE THIS FRIDAY NIGHT AND SATURDAY MORNING FROM 1135 PM

UNTIL 700 AM CDT.



HAIL TO 2 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 50

STATUTE MILES NORTH AND SOUTH OF A LINE FROM COLUMBUS NEBRASKA TO

35 MILES EAST OF KNOXVILLE IOWA.  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 258...



DISCUSSION...A BELT OF LOW-MIDLEVEL ASCENT IS SPREADING ESEWD OVER

NRN/CENTRAL NEB IN CONJUNCTION WITH AN EMBEDDED SPEED MAX...WHILE

THE SWLY LLJ IS BEGINNING TO INCREASE FROM KS INTO SE NEB.  THE NET

RESULT WILL BE A MORE FAVORABLE ENVIRONMENT FOR STORM DEVELOPMENT

ACROSS ERN NEB/SW AND S CENTRAL IA IN THE NEXT COUPLE OF HOURS...ON

THE NOSE OF THE LLJ AND ALONG THE SURFACE FRONT/INSTABILITY

GRADIENT.  RELATIVELY STRONG DEEP-LAYER SHEAR /EFFECTIVE BULK SHEAR

OF 60-70 KT/ AND A CORRIDOR OF MODERATE INSTABILITY WILL SUPPORT

STORMS WITH SUPERCELL STRUCTURES...AS WELL AS THE POTENTIAL FOR

EMBEDDED BOWS AS CONVECTION GROWS UPSCALE OVERNIGHT.  THE THREAT FOR

LARGE HAIL AND DAMAGING WINDS WILL PERSIST THROUGH THE PRE-DAWN

HOURS.



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

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

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

MOTION VECTOR 28030.





...THOMPSON

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