Temperatures struggled to 59 degrees Thursday at the three major Chicago weather
reporting locations -- O'Hare and Midway Airports and Northerly Island. It marked only
the second time this autumn the mercury has failed to reach or exceed 60 degrees, the
fewest sub-60-degree highs to occur this far into the fall season since 1966 when only
one high had remained below 60 degrees. The chill continues Friday with a second day
of 50s predicted -- the first time back-to-back 50s have occurred here in nearly 5
months.
Some lake-effect clouds greet Chicago as Friday dawns. Temperatures drop 27 degrees
in the first mile of the atmosphere -- supportive of lake cloud development. The steep
vertical temperature decline encourages air to rise from the lake surface, cool and
condense producing clouds. But with an easterly flow in place, winds travel over 80
miles of the lake, allowing little time for significant moisture to evaporate and fall as
rain.
60 OF PAST 80 YEARS HAVE PRODUCED MULTIPLE 70s BEYOND OCT. 17
A 70-degree high is predicted Sunday. Weather records indicate an average of four
70-degree days occurred beyond this date.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune
