Thunderstorms may flare later Saturday, developing in several clusters along a
southbound cold front that approaches this afternoon and passes with a wind shift to
the north in the evening.
Though hardly the muggy air mass that gripped the area earlier this week, the
atmosphere here will hold nearly 1.2 inches of evaporated water later Saturday. Surface
winds converging along the cold front while winds aloft diverge (move apart) signal that
thunderstorm-generating large-scale "lift" is being generated.
At the same time, faster-than-normal vertical temperature declines are to set up,
encouraging air to rise with gusto. Stronger than usual upper-level northwest steering
winds are likely to push along any thunderstorms that might erupt, increasing the
threat they'll become strong wind producers. The remnants of overnight thunderstorms
to Chicago's northwest may manage a sprinkle from mid-level clouds Saturday
morning, but the hope is most rainfall will await the front's arrival late Saturday.
CHICAGO'S 16-DAY STRING OF 80s AND 90s ENDS; COOLEST HIGH IN 2.5 WEEKS
Friday's 79-degree high may have ended this warm season's longest
80-degree-plus spell.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune
