I am having a discussion with a friend who says Chicago’s warmest month is August, on average. I say it’s July. We have agreed to take your word, and there is money riding on your answer.
You are correct: July is Chicago’s warmest month. With an average temperature of 75.9 degrees, July stands ahead of August’s 74.1 degrees. June ranks third warmest, at 71.0 degrees. September follows in fourth place, with 66.4 degrees. May is fifth, at 60.9 degrees. (These are Midway Airport temperature averages. Temperature averages at O’Hare International Airport run about two degrees cooler.) Average temperatures given here are for the 30-year period 1981-2010. Average temperatures (and the averages of all other weather variables, such as precipitation and snowfall) will be updated in 2021 to include the period 1991 -2020.