NASHVILLE, Tenn. (AP) — A massive winter storm made for a brutal travel day Sunday, with widespread cancellations and delays at some of the nation’s busiest airports.

Widespread snow, sleet, and freezing rain threatened nearly 180 million people, encompassing more than half of the U.S. population, stretching from the southern Rocky Mountains to New England. The storm moved into the Northeast Sunday, initially bringing about 1 to 2 feet (30 to 60 centimeters) of snow from Washington to Boston.

Flight cancellations soared over the weekend, with over 11,400 flights grounded on Sunday alone, according to FlightAware. This event marks the highest level of cancellations experienced since the onset of the pandemic, as major airports in the Northeast faced significant disruptions.

LaGuardia Airport in New York City was shuttered temporarily, with the FAA reporting that it would remain closed throughout the afternoon. In Philadelphia, 94% of flights were canceled, followed closely by LaGuardia at 91%, and JFK Airport saw around 80% cancellations as well.

Ronald Reagan Washington National Airport announced all airlines had canceled departing flights for the day, totaling around 421 flights. The impact was felt in major flight hubs such as Dallas-Fort Worth and Atlanta, the latter being the busiest airport in the nation.

Travelers affected by the storm are advised to reach out to their airlines for information on rebooking. Most carriers will rebook passengers on later flights without additional fees, contingent on seat availability, but there are no guarantees for flights on partner airlines.

Despite the chaos, airlines are required to provide refunds for canceled flights, even for non-refundable tickets, ensuring that travelers retain some recourse in the face of widespread cancellations.

The recovery from these extensive flight disruptions may take several days, as cascading delays could affect travel plans even outside of the directly impacted regions.