National Weather Service officials issued a dense fog advisory Saturday morning as visibility was less than a quarter mile in some areas in Chicago.
The advisory remains in effect until noon, officials said.
Saturday temperatures are expected in the high 40s, and the warmer temperatures will stick around for Christmas Day on Monday.
Officials cautioned driving conditions could become hazardous Saturday due to low visibility.
Afternoon conditions at Midway Airport are patchy drizzle with dense fog at 47 degrees. At O’Hare International Airport conditions are the same at 48 degrees.
Monday, temperatures are expected to hit 52 degrees, officials said.