Historically, which month in Chicago has produced the most tornados?

Dear Tom,
Historically speaking, which month in Chicago has produced the most tornados? Also, are there any patterns in tornado severity based on the time of year?
John Holden Chicago Edgewater
Dear John,
Based on the city’s tornado climatology dating back to 1950, June leads all other month with 30 percent of all recorded tornadoes. Runner up months are May with 19 percent of all twisters and April with 18 percent. The remaining nine months all register below 10 percent ranging from nine percent in August to 1 percent or less in the meteorological winter months of December, January and February. When considering significant tornadoes (EF-2 or stronger), April leads all other months, followed by June, August and November. The area’s strongest twister, the F-5 Plainfield storm, occurred on August 28, 1990 tragically taking 29 lives.

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