As wind chills dipped well-below zero Friday, the water on Lake Michigan changed dramatically.
Photos from the National Weather Service show the water over a 24-hour period. The first image shows steam coming off the water, but little-to-no ice formed.
By Friday morning, however, the water appeared covered in ice - and not just any ice.
"The ice does not appear to be solid - lots of 'pancake ice' out there," the NWS tweeted.
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Chicago reached a low temperature of -1 degrees Friday morning, the first sub-zero temperature of the season, which was also met with wind chills near -14 degrees.
The last time temps were that cold in the city was feb. 14, 2021, which saw a low of -5 degrees, NWS reported.
Other counties across the Chicago area also reported dangerously cold wind chills Friday morning, with a wind chill advisory in effect until 9 a.m. for many.
"The cold wind chills could cause frostbite on exposed skin in as few as 30 minutes," the advisory warned.
Residents were urged to bundle up and to spend as little time outdoors as possible.