

586 

WWUS20 KWNS 180921

SEL8

SPC WW 180921

IAZ000-NEZ000-SDZ000-181400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 458

NWS STORM PREDICTION CENTER NORMAN OK

420 AM CDT THU JUN 18 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHWEST IOWA

       EXTREME NORTHEAST NEBRASKA

       SOUTHEAST SOUTH DAKOTA



EFFECTIVE THIS THURSDAY MORNING FROM 420 AM UNTIL 900 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 45

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

SOUTHWEST OF YANKTON SOUTH DAKOTA TO 20 MILES SOUTHEAST OF

SPENCER IOWA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU8).



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 454...WW 455...WW

456...WW 457...



DISCUSSION...SMALL BUT INTENSE COMPLEX OF TSTMS MOVING ACROSS NRN

NEB WILL MOVE TO NWRN IA OVER THE NEXT COUPLE OF HOURS WITH SOME

POTENTIAL FOR WIND DAMAGE AND HAIL. THIS COMPLEX IS BEING SUPPORTED

BY WEAK LARGER SCALE HEIGHT FALLS AND MID LEVEL JET STREAK

ASSOCIATED WITH LOW AMPLITUDE SHORT WAVE TROUGH. ABUNDANT

INSTABILITY FEEDING STORM UPDRAFTS ON THE EDGE OF PLAINS CAPPING

INVERSION...COMBINED WITH MORE THAN ADEQUATE SHEAR...SHOULD ALLOW

THE COMPLEX TO MAINTAIN INTENSITY AND INTEGRITY AS IT SPREADS ACROSS

THE MO RIVER VALLEY EARLY TODAY.



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 550. MEAN STORM

MOTION VECTOR 26035.





...CARBIN

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