

053 

WWUS20 KWNS 271947

SEL7

SPC WW 271947

IAZ000-ILZ000-MOZ000-WIZ000-280300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 527

NWS STORM PREDICTION CENTER NORMAN OK

240 PM CDT SAT JUN 27 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       EASTERN IOWA

       NORTHERN ILLINOIS

       EXTREME NORTHEASTERN MISSOURI

       SOUTHERN WISCONSIN



EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 240 PM UNTIL

1000 PM 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 70

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

SOUTHEAST OF ROCKFORD ILLINOIS TO 55 MILES SOUTHWEST OF CEDAR

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

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU7).



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 525...WW 526...



DISCUSSION...STORMS ARE EXPECTED TO INCREASE IN NUMBER AND INTENSITY

AS UPPER JET AND COLD FRONT SPREAD IN FROM THE WEST. AIR MASS OVER

IOWA HAS BECOME STRONGLY UNSTABLE AS TEMPERATURES HAVE WARMED INTO

THE LOWER 90S...WITH DEWPOINTS IN THE MID 70S. THIS AIR MASS WILL

SPREAD EWD INTO NRN IL AND SRN WI THROUGH THE AFTERNOON. THE DEGREE

OF INSTABILITY AND DEEP LAYER SHEAR INCREASING TO 30 TO 40 KT SHOULD

SUPPORT STORMS WITH SOME MID LEVEL ROTATION AND HAIL. ALSO...THE

STORMS MAY CONSOLIDATE INTO A LINE ALONG THE FRONT...AND GIVEN THE

UNIDIRECTIONAL WLY WINDS ABOVE THE BOUNDARY LAYER...DAMAGING WINDS

WOULD ALSO BE EXPECTED.



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 27025.





...IMY

