

000 

WWUS20 KWNS 211702

SEL4

SPC WW 211702

IAZ000-MNZ000-WIZ000-220000-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 434

NWS STORM PREDICTION CENTER NORMAN OK

1200 PM CDT THU JUN 21 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHERN AND CENTRAL IOWA

       SOUTHERN AND CENTRAL MINNESOTA

       SOUTHWESTERN WISCONSIN



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM NOON UNTIL 700

PM CDT.



HAIL TO 3 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 85

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

SOUTHWEST OF FAIRMONT MINNESOTA TO 40 MILES NORTH NORTHEAST OF

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

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU4).



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 432. WATCH NUMBER 432 WILL NOT

BE IN EFFECT AFTER NOON CDT. CONTINUE...WW 433...



DISCUSSION...LARGE AREA/CLUSTER OF STRONG TO SEVERE THUNDERSTORMS IS

EXPECTED TO EVOLVE ACROSS WW THIS AFTERNOON...MOST LIKELY SPREADING

ESEWD AS A LINEAR MCS.  AIR MASS FEEDING THIS SYSTEM...SOUTH OF A

SURFACE FRONT LYING E-W ACROSS SRN MN...WILL BECOME STRONGLY

UNSTABLE.  COMBINED WITH 30-40 KT DEEP LAYER SHEAR...THIS WILL

INCREASE THE RISK OF LARGE HAIL AND DAMAGING WINDS INTO THE EARLY

EVENING...WITH POTENTIAL FOR WIDESPREAD SEVERE THREAT DEVELOPING

ACROSS WW.  IN ADDITION TO A LARGER SEVERE MCS...PARAMETERS WILL

ALSO FAVOR SUPERCELLS ESPECIALLY WITH ANY ISOLATED CELLS NEAR THE

FRONT.



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

TO 3 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

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

MOTION VECTOR 31035.





...EVANS

