The temperature dipped below zero overnight at O'Hare International Airport, the earliest that has happened here since 1995. The cold will hold through the week, bringing a burst of snow in time for the morning rush Wednesday.
The temperature fell to one degree below zero (-18C) around 12:55 a.m., according to the National Weather Service. That's the earliest subzero readings here since a low of minus 4 on Dec. 9, 1995.
By 7 a.m., the temperature had climbed to 8 degrees at O'Hare but the wind chill was 9 degrees below zero. The coldest temperature -- 4 degrees -- was recorded in Waukegan with a wind chill of minus-16F.