How does the difference between Chicago’s average daily high and low temperature vary between summer and winter?

This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.

Dear Tom,
How does the difference between Chicago’s average daily high and low temperature vary between summer and winter? What are the extremes?
—Terry Costlow Morton Grove
Dear Terry,
Comparing the average temperatures at the warmest and coldest times of the year, the typical winter span is 15 degrees in the Jan. 11-26 period, with an average high/low of 31/16. That difference increases to 21 degrees in the July 9-15 time frame, with an average high/low of 85/64. We had Chicago climatologist Frank Wachowski check the historic extremes, and he noted that the greatest calendar day high/low spread was 52 degrees on Feb. 8, 1900, when the mercury dropped to 10 after a high of 62. The least is zero, recorded just once on Feb. 6, 1942, with a high/low of 35/35. That rarity occurred during a 30-hour period of unchanged temperatures from 9 p.m. Feb. 5 through 3 a.m. Feb. 7.