CHICAGO (AP) -- As the winter's first major snowstorm continues to move across Illinois, airlines canceled more than 500 flights at Chicago airports.

The Chicago Department of Aviation said Thursday evening that more than 400 flights were canceled at O'Hare International Airport and delays from deicing were averaging 20 minutes. Southwest Airlines plans to resume flights at 6 p.m. after canceling more than 100 flights at Midway International Airport earlier in the day.

The National Weather Service in northern Illinois predicts between 6 and 8 inches of snow in Chicago and Joliet and 4 to 6 inches in Rockford, Dixon, LaSalle and Pontiac. Between 2 and 5 inches of snow are forecast in central Illinois.

Ice and snow covered roads were reported around Freeport, the Quad Cities, Bloomington and Jacksonville.