Just chilly enough to activate lake sprinkles/flurries later today
Chilly air is reinforced by northeast winds Saturday. While hardly a perfect lake-effect set-up, the flow may tap just enough moisture to bring a few sprinkles ashore later this afternoon. This year's abnormally mild fall has kept Lake Michigan comparatively "warm," which is why any lake-effect precipitation later today is likely to occur in liquid form. A late-week satellite analysis of surface water temperatures by NOAA's Great Lakes Environmental Research Laboratory puts Lake Michigan at 48 degrees. The warm water adds enough heat to the lower atmosphere to melt snowflakes to raindrops, an effect which nighttime cooling may override Saturday night.
Friday's 41-degree high was the second coldest this autumn. That reading followed the coldest overnight lows in 7-plus months -- including 17 degrees at Sugar Grove and Lincolnshire. The chilly air mass sent temps 700 miles to the south at Vicksburg, Miss., to 24 degrees Friday morning -- a reading which equaled Chicago's official 24-degree low at O'Hare.
--By Tom Skilling, WGN-TV Chief Meteorologist