In US, hundreds of flights into and out of Chicago's O'Hare and Midway airports were canceled as a winter storm system dumped moderate to heavy snow on the Upper Midwest and Lower Great Lakes regions before heading toward the US Northeast. <br/><br/>A winter storm warning was in effect in the Chicago area yesterday afternoon, with total accumulations of up to 10 inches expected by midnight CST, the National Weather Service said. It warned of difficult driving conditions in and around the country's third-biggest metropolitan area, where snow began falling on Saturday afternoon.<br/><br/>According to the Flightaware tracking service, more than 1,200 flights into and out of O'Hare were canceled yesterday afternoon, while nearly 200 Midway flights were scratched. Representatives of the airport and the airline could not be reached immediately to confirm the reports.