A late-winter storm barreled through the Midwest, snarling air travel in and out of Chicago, and it will soon take aim at busy airports around Washington, D.C. By late morning Tuesday, more than 1,200 flights had been canceled, almost all at Chicago's O'Hare and Midway airports. The airlines were already looking one day ahead and cutting flights in the storm's path. They had already canceled about 450 flights on Wednesday, mostly at Dulles and Reagan National airports in the Washington area, according to FlightAware.com. The storm blew out of Montana on Sunday, raced across the Dakotas and Minnesota on Monday and was expected to dump 10 inches of snow on Chicago. Brian Korty, a forecaster with the National Weather Service, said the storm was likely to arc across West Virginia and could dump a foot of snow on Dulles Airport in Washington's Virginia suburbs and six inches at Reagan National and Baltimore-Washington airports. It might start as rain late Tuesday but switch to snow by Wednesday morning, he said. "The wind will be blowing, and visibility will be an issue," Korty said. The forecaster said that airports in New York and Philadelphia stood a better chance of dodging the brunt of the storm. United Airlines, which has a big operation at Dulles, offered travelers the option of rescheduling trips without paying the usual change fees. Passengers holding tickets for flights Tuesday or Wednesday to or from 27 airports in seven states from Ohio to Maryland could avoid the fees and difference in fares by beginning rescheduled trips by next Monday.