As the upper air flow changes to northwest over the Midwest, so too will the airmass near the surface. Gone now is the hot and humid airmass which set numerous records earlier in the week. A little cooler and drier airmass is in place today, Thursday, to be replaced by Friday with the first real push of autumn air out of Canada. The high pressure center will be right over the Midwest Saturday morning.
For the Chicago metro area, the record tying highs in the mid 90s will be replaced by highs only in the mid to upper 60s for Friday. This will represent a 30 degree temperature drop from Tuesday to Friday. Unfortunately, the front last night brought very little rain to the metro area. Only areas really well south of the metro area had rain amounts of 3/4 to 1 inch. Elsewhere rainfall ranged from a trace to only a tenth or two.
A very compact and isolated severe storm formed over the far south side of Naperville in northern Will county Wednesday afternoon. Hail ranging in size from 1 inch to golf ball was reported in the area from south Naperville through Bolingbrook to Romeoville. A very small area of very strong winds, a microburst, occurred over far southwest Cook county around the Lemont area. The graphic from the TMDW FAA doppler weather radar shows 70 knots (80.5 mph) just east of Lemont. Thankfully the really high speed winds lasted a very short amount of time. A complete list of reports can be found here.
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