A powerful blizzard ground air travel to a near halt at major airports serving New York City, Boston and Philadelphia on Monday. Disruptions are set to last through at least Tuesday, again testing carriers on how quickly they can recover at the tail-end of winter break.

Much of the East Coast from Maryland to Maine was under a blizzard warning, with heavy snow totaling nearly two feet in parts of New Jersey and on Long Island, New York, as of Monday morning. High winds are expected to last throughout the day, the National Weather Service said. The NWS warned that travel will be treacherous, with blowing snow causing low visibility.

More than 3,800 flights on Monday, or 15% of the total scheduled U.S. departures, were canceled, according to aviation-data firm Cirium. Daily cancellations usually run around 1%.

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

Flight disruptions were set to continue on Tuesday, with around 40% of the flights at LaGuardia and New York’s John F. Kennedy International Airport canceled, with roughly the same amount canceled in Boston, according to FlightAware.

Airlines routinely cancel flights ahead of major storms to avoid having aircraft and crews out of place and to make it easier to restart operations after the storm passes.

American Airlines, Delta Air Lines, JetBlue Airways, Spirit Airlines and United Airlines waived fees and fare differences for passengers if they can travel as late as Feb. 26. Southwest Airlines said customers are eligible for a change without paying a difference in fare if they can rebook to fly or fly standby within two weeks.

The winter storm that hit much of the East Coast in January and was followed by bitter cold caused mass travel disruptions across a large swath of the U.S.

American had struggled to recover, drawing harsh criticism from flight crews, some of whom were stranded and had to sleep at airports, heightening tension between frontline employees and the company’s CEO, Robert Isom.

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