Airlines cancel thousands of flights due to a snow storm that paralyzes the East Coast

Ground air traffic was halted due to a strong snowstorm at major airports serving New York City, Boston, Philadelphia and other areas in the eastern United States on Monday. The disruptions are set to continue until at least Tuesday, once again testing carriers on how quickly they can recover at the end of the winter break.

Much of the East Coast from Maryland to Maine was under a blizzard warning, with heavy snow totaling about 2 feet in parts of New Jersey and Long Island, New York. The National Weather Service said strong winds were expected to continue throughout the day. The Meteorological Service warned that travel would be dangerous, as snowfall caused reduced visibility.

More than 4,800 U.S. departures were canceled Monday, or nearly 20% of all scheduled U.S. departures, as of 9:40 a.m. ET, according to aviation data company Cirium. Daily cancellations are typically around 1% of the day’s schedule. Nearly a quarter of incoming international flights have also been cancelled.

More than 1,000 departures and arrivals into and out of New York’s LaGuardia Airport, about 98% of the day’s schedule, were canceled on Monday. More than 90% of flights at Boston Logan International Airport and more than 80% of flights at Philadelphia International Airport and Newark Liberty International Airport in New Jersey were also cancelled.

Flight disruptions are scheduled to continue Tuesday, with about 40% of flights canceled at LaGuardia and John F. Kennedy International Airport in New York, with about the same amount canceled in Boston, according to FlightAware.

Airlines routinely cancel flights before major storms to avoid grounding aircraft and crews and to facilitate restarting operations after the storm passes.

American Airlines, Delta Airlines, JetBlue AirlinesSpirit Airlines and United Airlines Fees and fare differences have been waived for passengers if they can travel until February 26. Southwest Airlines Said customers are eligible to change without paying a difference in fare if they can rebook to fly or fly standby within two weeks.

A winter storm that struck much of the East Coast in January and was followed by extreme cold disrupted mass travel across a large swath of the United States.

American has struggled to recover, drawing intense criticism from flight crews who have been stranded and forced to sleep in airports, raising tensions between front-line employees and the company’s CEO, Robert Isom.

The storm cost the U.S. between $150 million and $200 million in revenue, the carrier said last month on an earnings call.