

064 

WWUS20 KWNS 091526

SEL2

SPC WW 091526

IAZ000-ILZ000-WIZ000-LMZ000-092300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 682

NWS STORM PREDICTION CENTER NORMAN OK

1025 AM CDT SUN AUG 9 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       EASTERN IOWA

       NORTHERN ILLINOIS

       SOUTHERN WISCONSIN

       LAKE MICHIGAN



EFFECTIVE THIS SUNDAY MORNING AND EVENING FROM 1025 AM UNTIL 600

PM CDT.



HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 80

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 45 MILES NORTHWEST

OF CEDAR RAPIDS IOWA TO 20 MILES EAST SOUTHEAST OF RACINE

WISCONSIN.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).



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 680...WW 681...



DISCUSSION...SEVERE STORM CLUSTER OVER CENTRAL IA IS EXPECTED TO

MOVE EWD/ENEWD AT 35-40 KT...WITH POTENTIAL FOR NEW UPDRAFTS TO

DEVELOP ON SRN FLANK OF THE OUTFLOW BOUNDARY AS IT ENCOUNTERS

INCREASING MOIST AND UNSTABLE AIR MASS.  VISIBLE IMAGERY SHOWS FEW

CLOUDS DOWNSTREAM OF THE CONVECTION WITH STRONG DIABATIC HEATING

EXPECTED THIS AFTERNOON...WHICH WILL CONTRIBUTE TO ADDITIONAL

DESTABILIZATION WITH MLCAPE REACHING 2500-3500 J/KG. DEEP LAYER

SHEAR WITHIN RIGHT ENTRANCE REGION OF MID/UPPER LEVEL JET WILL

ENHANCE CONVECTIVE SCALE ORGANIZATION AND INTENSITY...WITH

CONTINUING THREAT FOR DAMAGING WINDS AND LARGE HAIL.  UNIDIRECTIONAL

SHEAR ALSO INDICATES POSSIBILITY OF MESOSCALE BOW ECHO SYSTEM

DEVELOPMENT...AND IF THIS OCCURS THREAT FOR MORE WIDESPREAD DAMAGING

WIND EVENT WILL INCREASE.



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

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 70

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

MOTION VECTOR 25035.





...WEISS

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