An unusually potent early season cool spell, which is being forced south into the U.S. from the Canadian arctic by powerful northerly upper air winds, threatens to break a 22 year old record by producing a 39° low Saturday at O’Hare. The old record is 40° set in 1985. The incoming air mass is to become so unstable later today—e.g. temperatures within it are to decline so rapidly with height—that the sunshine predicted to follow daybreak clouds and showers is likely to encourage air to rise and cool producing new clouds and light showers by mid/late afternoon. Once the new overcast is in place, the day’s gusty NW winds import chilly air allowing temps to fall to the mid 50s by evening.
Winds diminish and skies clear overnight allowing temps to dive. Far west and NW suburban lows reach 33° by morning threatening the season’s first frost patches. The urban heat island is to modify cooling in the city enough to discourage frost.
--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.
