U.S. airlines have already canceled more than 6,000 flights Monday and Tuesday as a late-winter storm is expected to dump enough snow to disrupt travel in the Northeast.

Southwest Airlines, which carries more domestic passengers than any other airline, doesn't expect to operate any flights Tuesday at 14 airports stretching from Washington to Portland, Maine.

Tracking service FlightAware.com said Monday afternoon that more than 1,500 flights on Monday and more than 4,600 on Tuesday had been canceled.

Chicago is bearing the largest share of Monday's cancellations, while Tuesday's disruptions are hitting hardest in the East, from Washington to Boston including the New York City area.

The major airlines are waiving ticket-change fees that range up to $200 for customers who want to change their travel plans. Restrictions vary by airline.

Southwest has canceled more than 300 flights for Monday and nearly another 900 scheduled for Tuesday, according to FlightAware.

American Airlines and its American Eagle contractor Envoy Air together had canceled more than 300 flights Monday and 700 on Tuesday. JetBlue Airways, with major operations in Boston and New York, had already canceled more than 600 flights scheduled for Tuesday, FlightAware said.