Dear Tom, SLK
What is the latest date the year’s first 90 degrees has been officially reached at Chicago?
In 1875, the temperature in Chicago failed to reach 90, the only year in the 149 years of weather records dating back to 1871 that this has ever happened. The highest reading that year was 89 recorded on June 11. Eliminating that year from consideration, the city’s latest onset of 90s was in 1915, when the thermometer reached 90 on September 14, for the year’s lone occurrence. Of course, in both instances the official thermometer was located near chilly Lake Michigan. Since the official readings were moved inland in July,1942, the latest onset of 90s was on August 15, 2000, the first of only four that year. On the opposite side of the ledger, the city’s earliest onset of 90s occurred in 1930, when back-to-back highs of 90 were recorded on both April 10 and 11.