Dear Tom,
Has Chicago ever had a year where thunderstorms occurred in all twelve months?
—Jim Kaplan, Joliet
Dear Jim,
Checking the record books dating back to 1871, it has only happened twice, first in 1950 and again in 1975. Chicago averages about 38 thunderstorm days a year, with the vast majority of them occurring in the warmer time of the year. Winter thunderstorms do occur, but at a much lower frequency, and on rare occasions they are accompanied by snow. In 1950, the annual thunderstorm day total was actually below average, with just 35 on the books, but the city did log at least one in every month. Thunderstorms in 1975 were prolific with the year’s total an all-time record of 66. August led all months with 13 thunderstorm days, but the winter months were also quite active with four in January, one in February and three in December.