LAS VEGAS (AP) — 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 its data shows that Sunday will be the highest cancellation event since the pandemic, with over 29% of all U.S. departing flights axed.

[Live updates: Winter Storm Fern’s icy aftermath]

My flight was canceled. Now what?

If you’re already at the airport, get in line to speak to a customer service representative. If you’re still at home or at your hotel, call or go online to connect to your airline’s reservations staff. Either way, it helps to also research alternate flights while you wait to talk to an agent.

Most airlines will rebook you on a later flight for no additional charge, but it depends on the availability of open seats.

Can I get booked on another airline?

You can, but airlines aren’t required to put you on another carrier’s flight. Some airlines, including most of the biggest carriers, say they can put you on a partner airline, but even then, it can be a hit or miss.

Am I owed a refund?

If your flight was canceled and you no longer want to take the trip, or you’ve found another way to get to your destination, the airline is legally required to refund your money — even if you bought a non-refundable ticket. It doesn’t matter why the flight was canceled.

The airline might offer you a travel credit, but you are entitled to a full refund. You are also entitled to a refund of any bag fees, seat upgrades or other extras that you didn’t get to use.