I’m wondering what Chicago’s earliest and latest 100 and 90 degrees are?
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.