Chicago experiences higher temperatures longer than outlying suburbs due to the urban heat-island effect. Its location next to Lake Michigan’s warm waters explains why the city and nearby suburbs freeze later in the year than their farther-out counterparts.
Here’s a look back at when our area typically experiences its first freeze and first snowfall of fall.
First fall freeze
The earliest first freeze on record occurred Sept. 22, 1995, at O’Hare airport. The latest was Nov. 24, 1931.
The temperature didn’t fall at or below freezing until Nov. 20 in 2024. It happened on Oct. 31 in 2023.
“The first freeze, which is when the temperature drops at or below 32 degrees, typically occurs between Oct. 11 and Oct. 12 across the Chicago suburbs and Oct. 21 to Oct. 30 in the city and along the lakeshore,” Brett Borchardt, meteorologist for the National Weather Service’s Chicago office, told the Tribune.
Frost can develop on clear nights when the air temperature is in the mid-30s, but can be scattered. That’s why, former WGN-TV chief meteorologist Tom Skilling told the Tribune in 2018, the weather service “does not keep statistics regarding frost but instead uses the season’s first temperature of 32 (degrees) or lower to define the end of the growing season.”
First fall snow
Fall’s first measurable snowfall — you know, the stuff that sticks — arrived on Halloween in 2023. Since more than a tenth of an inch accumulated, then that counted as “measurable.” If less than a tenth of an inch is observed at O’Hare then that counts as a “trace” amount — even if it doesn’t stick. Whether a trace amount of snow is a “first snow” is up for debate.
It was a double whammy — fall’s first freezing temperature and first snowfall. At 3:51 a.m., Oct. 31, 2023, the temperature was 30 degrees at O’Hare International Airport, the city’s official recording site.
It was just the 10th time in local weather history the two milestones were achieved on the same calendar day, said Jake Petr, a meteorologist in the National Weather Service’s Chicago office.
It’s also just the eighth time snow has fallen in Chicago on Halloween — and only the third time a measurable snowfall has been recorded on Oct. 31.
Sources: National Weather Service; Tribune reporting and archives
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