Dear Tom,
We’ve had so few 90s this summer. Have we ever had a summer without any?
Adrian P., Chicago
Dear Adrian,
It’s happened only once, in 1875. The summer of 1915 was on track to be the second, but a late-season hot spell sent the mercury surging to 90 degrees Sept. 15, the only 90 of the year.
In both of those years, the city observations were taken downtown close to Lake Michigan’s cooling breezes, where highs reached the upper 80s on several days, so it is almost certain that additional 90s were recorded at inland locations.
Since the official thermometer was moved inland to Midway Airport in 1942 and then to O’Hare in 1980, the fewest number of 90-degree days in a year has been two in 1979.
Other years with few 90s include 2004 with three, and 1967, 2000 and 2009, all with four.
