

588 

WWUS20 KWNS 180452

SEL5

SPC WW 180452

IAZ000-ILZ000-MNZ000-WIZ000-181100-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 455

NWS STORM PREDICTION CENTER NORMAN OK

1155 PM CDT WED JUN 17 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       MOST OF IOWA

       EXTREME NORTHWEST ILLINOIS

       SOUTHEAST MINNESOTA

       SOUTHWEST WISCONSIN



EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 1155 PM

UNTIL 600 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 105

STATUTE MILES EAST AND WEST OF A LINE FROM 50 MILES NORTHEAST OF

MANKATO MINNESOTA TO 20 MILES SOUTHEAST OF KNOXVILLE IOWA.  FOR A

COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE

UPDATE (WOUS64 KWNS WOU5).



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

TORNADO WATCH NUMBER 449. WATCH NUMBER 449 WILL NOT BE IN EFFECT

AFTER 1155 PM CDT. CONTINUE...WW 447...WW 448...WW 450...WW

451...WW 452...WW 453...WW 454...



DISCUSSION...THUNDERSTORMS CONTINUE IN THE BROAD ZONE OF LOW-LEVEL

WARM ADVECTION CENTERED OVER IA.  A RESERVOIR OF MODERATE-STRONG

INSTABILITY REMAINS TO THE SW OF THE WARM FRONT NEAR THE MS

RIVER...AND IN ADVANCE OF THE ONGOING STORMS ACROSS WRN/CENTRAL

IA...AND THIS INSTABILITY WILL MAINTAIN A SEVERE THREAT OVERNIGHT.

VERTICAL SHEAR IS STILL FAVORABLE FOR SUPERCELLS...THOUGH SLOW

STABILIZATION OF NEAR-SURFACE LAYER SUGGESTS THAT LARGE HAIL AND

DAMAGING WINDS WILL BE THE PRIMARY THREATS.



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 27020.





...THOMPSON

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