CHICAGO (AP) -- A winter storm whipping across the region has forced the cancellation of more than 700 flights at Chicago's airports.

The Chicago Department of Aviation says more than 600 flights in and out of O'Hare International Airport have been canceled Friday. Airlines at Midway Airport have canceled more than 100 flights.

The National Weather Service says up to 8 inches of snow could fall by Friday evening.

Chicago deployed its full fleet of 278 snow plows, but they were left inching along with commuters headed home for the day in heavy rush-hour traffic.

The weather service has issued a winter storm warning that's in effect until late Friday.