Massive winter storm grounds hundreds of flights across the U.S.

Airlines canceled hundreds of flights for the second time in a week ahead of a massive winter storm that’s forecast to impact areas from Texas to New England.

More than 1,400 U.S. flights were canceled on Wednesday and close to 1,700 scheduled for Thursday, according to flight-tracking site FlightAware.

The National Weather Service said heavy freezing rain is expected to accumulate from Texas through the Ohio River Valley as well as heavy snow through the Upper Midwest.

Southwest Airlines canceled nearly 400 Wednesday flights, or 12% of its schedule, and 517 flights, or 15%, scheduled for Thursday, according to FlightAware. It suspended flights at its home hub of Dallas Love Field on Thursday. American Airlines canceled more than 350 mainline flights scheduled for Wednesday. A quarter of the departures scheduled for Thursday from Dallas/Fort Worth International Airport were canceled.

Airlines including Southwest, American, Delta and United said they would waive fare differences for travelers who plan to rebook flights because of the storm.

Last week, airlines scrubbed more than 4,000 U.S. flights due to another storm that hit the Northeast. Carriers generally cancel flights ahead of large weather systems to avoid passengers and crews getting stranded at airports, making it easier to reset the operation the following day.