How much do Chicago’s daily temperatures change during the winter?

Dear Tom,
How much do Chicago’s daily temperatures change during the winter?
— William Girard, Shorewood
Dear William,
One of the characteristics of Chicago’s climate is rather large temperature fluctuations during the year (larger, in general, than locations in the Eastern and Southern U.S., but not as large as locations in the Western and Northwest U.S.). Chicago’s average daily temperatures at Midway Airport range from a high of 85 degrees and low of 68 in mid-to-late July to a low of 31/18 in mid-to-late January. Meteorological winter (December through February) is the coldest season, of course, but the coldest portion of winter is mid-to-late January, on average. Temperatures decline from 40/28 degrees (average daily high and low) on Dec. 1 to 31/18 in mid-to-late January, then begin gradually moderating to 41/26 degrees by the end of February.