What is Chicago’s latest calendar date for a sub-zero temperature?

by: Tom Skilling, WGN-TV Weather Team

Posted: Feb 22, 2023 / 04:58 PM CST

Updated: Feb 23, 2023 / 09:00 AM CST

Dear Tom,

What is Chicago’s latest calendar date for a sub-zero temperature?
Mike Foos, Chesterton, Indiana

Dear Mike,

Historically, Chicago’s subzero season runs from late November to early March, according to Chicago climatologist Frank Wachowski. The city’s earliest subzero temperature occurred Nov. 23, 1950, a frigid Thanksgiving morning that went to 1 below. Subzero cold that early in the season is unusual, with the bulk of the city’s negative temperatures occurring from mid-December through mid-February, peaking during February’s opening days, which coincides with the period of most persistent snow cover. Early March usually marks the end of below zero weather here, but the 1-below-zero reading on March 22, 1888, is the city’s latest on record.