A powerful winter storm battered air travel across the United States on Sunday, triggering widespread flight cancellations and delays at many of the country’s busiest airports.

The National Weather Service said snow, sleet and freezing rain threatened nearly 180 million people, more than half of the US population, across a vast corridor stretching from the southern Rocky Mountains to New England. After moving through the South, the storm advanced into the Northeast on Sunday, with forecasts calling for roughly 1 to 2 feet of snow from Washington to New York and Boston.

Flight-tracking website FlightAware reported that more than 11,400 flights were canceled on Sunday. Aviation analytics firm Cirium said the disruption marked the largest cancellation event since the Covid-19 pandemic.

By Sunday afternoon, cancellations dominated flight schedules at major airports, particularly in the Northeast. New York’s LaGuardia Airport suspended operations until 8pm, according to the Federal Aviation Administration. In Philadelphia, 94 percent of flights were canceled, while LaGuardia saw 91 percent of flights grounded. John F. Kennedy International Airport in New York canceled about 80 percent of its flights. All departing flights were also canceled at Ronald Reagan Washington National Airport.

Major hubs in Dallas-Fort Worth, Charlotte and Atlanta also reported significant disruption.

American Airlines canceled more than 1,790 flights, while Delta, Southwest, United and JetBlue also reported heavy losses to their schedules.

Aviation expert Vikrant Vaze said recovery could take days, warning that cascading delays may affect travelers even outside storm-hit regions.