How many days per year does Chicago have high temperatures in 70s

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Dear Tom,
How many days per year does Chicago have high temperatures in 70s, which is an absolutely perfect temperature range?
— Kris Keller

Dear Kris,
On average, Chicago experiences 59 days per year with high temperatures in the 70s. That figure is calculated from 88 years (1929 through 2016) of daily readings at Midway Airport. Highs in the 60s occur on 47 days, in the 80s on 62 days and in the 90s on 23 days.
With the exception of January, readings in the 70s have occurred in every month of the year, but they tend to be concentrated in two periods: mid-May to mid-June and September. From late June through August, highs in the 80s and 90s are more frequent.
It should be noted that many people enjoy summer temperatures warmer than the 70s, and some outdoor activities (like swimming) require higher readings.

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