What are the earliest and latest dates of Chicago’s 90-degree temperatures of the season?

Dear Tom,
What are the earliest and latest dates of Chicago’s 90-degree temperatures of the season? Have there been any years without any?
Nick Recchia, River Grove
Dear Nick,
In 148 years of official Chicago temperature records dating from 1871, only a single year has failed to produce a temperature of 90 degrees: 1875. The highest temperature that year was 89 degrees, registered on June 11. The observation station then was located in downtown Chicago, very near Lake Michigan. It is likely that temperatures farther inland did record 90-degree readings, but nevertheless 89 degrees is the official measurement. The earliest 90-degree reading occurred in 1930, on April 10, at the University of Chicago, which was at the time the official observation station. The latest occurrence was on October 6, 1963, at Midway Airport, when the temperature jumped to 94 degrees.

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