Classifying a summery day as eighty degrees or higher, which year featured Chicago’s longest summer with the most calendar days between first and last occurrence?
In a typical Chicago year the season’s first 80 occurs around April 26 and the last on October 4; a 162 day period. Chicago climatologist Frank Wachowski noted that the longest period from the first to last 80 occurred in 1990. It covered 207 days from a high of 81 on March 12 to an 84 on October 6. Historically, the city’s earliest 80 occurred on March 3, 1974 and the latest on November 1, 1950. Not surprisingly, the city’s shortest 80-degree season took place in 1875, when the city’s official thermometer was located downtown near the lake. That season spanned just 91 days from a high of 89 on June 11 to a high of 80 on September 9.