Aviation officials say low visibility is causing flight delays of up to an hour at Chicago's O'Hare International Airport.
They say 50 O'Hare flights have been canceled so far.
The cancelations come amid Illinois' first snowstorm of the season. Weather service officials say it could dump up to 8 inches of snow in some northern counties.
A winter storm warning covering all of north-central Illinois is in effect until noon tomorrow. Central Illinois may see around 5 inches of snow.
Officials warn that drifting snow and freezing temperatures could make travel hazardous for those returning home from the holidays.