What has been, the highest overnight temperature ever recorded in Chicago?

Dear Tom,

What has been, the highest overnight temperature ever recorded in Chicago?

Thanks,
Dennis Cusumano
Winthrop Harbor

Dear Dennis,

Chicago’s highest minimum temperature was a stifling 85 degrees, recorded on July 29, 1916. It occurred during an extended heat wave, in an era that preceded air conditioning, when the city’s official temperature failed to drop below 80 degrees for 147 hours from July 25-31, while maximum temperatures peaked as high as 102. It should be noted, that in 1916, the city’s official temperatures were taken downtown at the old U.S. Court House on Dearborn St, though the city’s heat island effect was far less than today. Overnight lows of 80 degrees or higher are extremely rare in Chicago, having occurred at the city’s official station on only 33 days since records began back in 1871, including an 81-degree low earlier this summer on July 19.

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