Chicago’s earliest and latest 100 and 90 degrees

Dear Tom,
I’m wondering what Chicago’s earliest and latest 100 and 90 degrees are?

Larry Paarlberg

Dear Larry,
We asked Chicago weather historian to find the answer to your question. Wachowski reported that Chicago’s “high-heat” season, based on official readings, has begun as early as April 10 and 11 when the city recorded back-to-back early-season highs of 90 in 1930 and has extended to as late as October 6 when the mercury soared to 94 in 1963. Chicago’s triple-digit season is noticeably shorter with the city’s earliest occurrence on June 1 with a high of 102 in 1934. The latest-in-the season 100 occurred on September 7 when the temperature topped out at 100 in 1960. Chicago’s all-time highest temperature is 105 recorded on July 24, 1934 at the official University of Chicago site, but unofficially Midway Airport logged a scorching 109 the previous day.