Based on past history, what date of the year is it most likely to snow in Chicagoland?

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Dear Tom,
Based on past history, what date of the year is it most likely to snow in Chicagoland?
— Leslie Rosenwinkel,
Glen Ellyn
Dear Leslie,
Based on data dating to the winter of 1884-85, Chicago’s historical season for measurable snowfall (at least 0.1 inche) extends from Oct. 12 through May 11.
We asked Chicago climatologist Frank Wachowski to crunch the numbers, and he reported that the city’s dates with the most frequent measurable snowfalls over that period were Jan. 13 with snow on 46 days, Jan. 26 with 45 days, Feb. 6 with 44 and Christmas Day with 43.
The winter dates with the fewest occurrences of measurable snowfall were Dec. 2, Dec. 7 and Jan. 10 with 20, and Feb. 27 with 22 days.

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