AREAS AFFECTED...SWRN-SRN WI/NRN IL AND EXTREME NERN IA
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 240832Z - 240930Z
PROBABILITY OF WATCH ISSUANCE...40 PERCENT
SUMMARY...A LINE OF TSTMS MOVING SEWD AT 40-44 KT WILL REACH FAR
NWRN-NRN IL AROUND 10Z...AND IF THIS ACTIVITY REMAINS IN TACT...IT
WILL REACH THE CHICAGO METRO AREA BETWEEN 11-12Z. MARGINALLY SEVERE
WIND GUSTS WILL BE POSSIBLE IN THE SHORT TERM...WITH THIS ACTIVITY
BEING MONITORED FOR ANY FURTHER UPSCALE GROWTH AND GREATER SEVERE
THREAT.
DISCUSSION...AT 0810Z...REGIONAL RADAR IMAGERY SHOWED A SEWD MOVING
LINE OF TSTMS EXTENDING FROM SAUK COUNTY TO CRAWFORD COUNTY WI.
THIS ACTIVITY WAS LOCATED ALONG AND JUST NE OF A STALLED SURFACE
BOUNDARY AND WITHIN THE ERN EXTENT OF STEEP MIDLEVEL LAPSE RATES
CONTRIBUTING TO A WNW-ESE CORRIDOR OF MODERATE INSTABILITY EXTENDING
FROM NRN IA TO FAR SRN WI AND NRN IL. AREA VWPS INDICATED 40 KT
NWLY MIDLEVEL WINDS...WITH SWLY LOW LEVEL WINDS INCREASING SOME INTO
NRN IA /AT 25-30 KT/. GIVEN THE NWLY MEAN FLOW AND EFFECTIVE BULK
SHEAR AROUND 40 KT WITH VECTORS PARALLEL TO THE SURFACE
BOUNDARY...STORM MODE SHOULD REMAIN LINEAR. THIS LINE OF STORMS
WILL PROGRESS SEWD WITH RAP FORECAST SOUNDINGS SUGGESTING A LAYER OF
DRY AIR IN THE LOW LEVELS THAT COULD SUPPORT AN ENHANCEMENT IN
DOWNDRAFT MOMENTUM DUE TO EVAPORATIVE COOLING. THIS COMBINED WITH
THE FORWARD SPEED OF 40 KT WILL BE SUFFICIENT FOR AT LEAST
MARGINALLY SEVERE WIND GUSTS AS HAVE BEEN RECENTLY OBSERVED IN FAR
NERN IA AND SWRN WI WITH GUSTS RANGING FROM 47-52 KT.
..PETERS/THOMPSON.. 07/24/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...LOT...MKX...DVN...ARX...
LAT...LON 43158975 42148781 41208816 41198913 41779024 42509094
43158975
