A massive winter storm set the stage for a brutal travel day Sunday, with airlines warning of widespread cancellations and delays at some of the nation’s busiest airports. More than 13,500 flights have been canceled across the U.S. since Saturday, according to flight-tracking site FlightAware. About 9,600 of those were scheduled for Sunday. Aviation analytics company Cirium says their data shows that Sunday will be the highest cancellation event since the pandemic — with over 29% of all U.S. departing flights axed.