It's not common for such chilly air to hit this early. Saturday morning's predicted 39 degrees at O'Hare didn’t occur a year ago until Sept. 29 at the site -- that's two weeks later than today -- and has occurred on average on or about Oct. 3 over the past 136 years. The 39 degree low would set a new record for the date, breaking the old record of 40 degrees set 22 years ago in 1985.
Diminishing winds have produced the area's most dramatic cooling from the Fox Valley and McHenry County westward. It's a development which has favored frost formation in some west suburban locations. In stark contrast, the same chilly air's interaction with still-warm Lake Michigan waters has led to lake-effect clouds east of Chicago and threatens light rain showers from sections of LaPorte County eastward.
Northern Minnesota was home to the Midwest's first flurries of the season Friday, near International Falls and in the state's Arrowhead region. Chilly air produced a 22 degree low at Williston, N.D., early Friday.
--By Tom Skilling, WGN-TV Chief Meteorologist
WGN-TV Chief Meteorologist Tom Skilling and the WGN Weather Center staff provide daily coverage of weather in the Chicago area.
