

462 

WWUS20 KWNS 050147

SEL6

SPC WW 050147

IAZ000-ILZ000-LMZ000-050700-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 616

NWS STORM PREDICTION CENTER NORMAN OK

850 PM CDT TUE SEP 4 2012



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       EAST CENTRAL IOWA

       NORTHERN ILLINOIS

       LAKE MICHIGAN



EFFECTIVE THIS TUESDAY NIGHT AND WEDNESDAY MORNING FROM 850 PM

UNTIL 200 AM CDT.



HAIL TO 1.5 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 30

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 25 MILES SOUTH OF

DUBUQUE IOWA TO 105 MILES EAST OF ROCKFORD ILLINOIS.  FOR A

COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE

UPDATE (WOUS64 KWNS WOU6).



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 614...WW 615...



DISCUSSION...THE MCS OVER SE WI HAS SHOWN A TENDENCY TO ACCELERATE

SEWD IN THE PAST HOUR...WHILE UPSTREAM SEVERE STORMS ACROSS SW WI/NE

IA SHOULD LIKEWISE MOVE SEWD WITH THE COMPOSITE OUTFLOW BOUNDARY.

GIVEN THE PRESENCE OF STEEP MIDLEVEL LAPSE RATES AND MLCAPE AOA 2000

J/KG PER 00Z DVN SOUNDING...THE THREAT FOR AT LEAST ISOLATED

DAMAGING WINDS/LARGE HAIL SHOULD SPREAD INTO NRN IL BEFORE THE

STORMS WEAKEN LATER TONIGHT.



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

TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM

MOTION VECTOR 31025.





...THOMPSON

