Airlines cancel more than 13,000 weekend flights as massive winter storm sweeps across the U.S.

Airlines canceled more than 13,000 U.S. flights this weekend as a massive winter storm swept across the country, bringing heavy snow, ice and sleet, followed by bitter cold.

More than 4,000 flights on Saturday were canceled, according to flight tracker FlightAware. Many of Saturday's cancellations were in and out of Dallas Fort Worth International Airport, with nearly 1,500 scrubbed flights, and at Dallas Love Field, with 190 cancellations, the majority of the schedule at each airport.

American Airlines, based in Fort Worth, Texas, had canceled 1,056 Saturday flights, more than a third of its mainline schedule and Southwest Airlines canceled 579 flights, or 20%, according to FlightAware.

U.S. flight cancellations more than doubled to nearly 9,100 on Sunday when the storm is expected to hit the mid-Atlantic and Northeast U.S. As of Saturday afternoon, most flights from Raleigh-Durham International Airport in North Carolina to Portland, Maine, were canceled. Major airline hubs were affected as far south as Atlanta, where Delta Air Lines is based.

Nearly 90% of Sunday flights were canceled at LaGuardia Airport in New York and 96% at Ronald Reagan Washington National Airport. More than 70% of flights at Newark Liberty International Airport in New Jersey and New York's John F. Kennedy International Airport, which have more international flights, were also canceled for Sunday.

Airlines routinely cancel flights ahead of a major storm to prevent planes, passengers and crew from getting stranded, which can worsen disruptions after severe weather moves out. January is a low season for travel generally but the vast storm was set to snarl travel for hundreds of thousands of people for days.

American, Delta, JetBlue Airways, Southwest Airlines, United Airlines and other U.S. carriers said they are waiving change and cancellation fees as well as fare differences to rebook for customers with tickets to and from more than 40 airports around the country. The waivers include restrictive basic economy tickets.

American said it was repositioning its airplanes and increasing staffing at major airports to help soften the impact of the storm and to "set the stage for a fast, safe recovery once conditions improve."

The National Weather Service is warning that the winter storm could affect hundreds of millions of people and is expected to "bring widespread heavy snow, sleet, and freezing rain from the Southern Rockies to New England through Monday."