(NewsNation Now) — Flight cancellations and delays continued throughout the weekend, causing frustrations for many air travelers.

By late Sunday evening, more than 1,300 flights within, into or out of the U.S. had been canceled, and almost 4,500 were experiencing delays, according to tracking service FlightAware.

Alaska Airlines was having a particularly tough day; as of 10:25 p.m. CT, the Seattle-based airline had canceled 111 flights, or 15% of its schedule.

Southwest, which has experienced numerous cancellations and delays in the past week, had canceled the most flights among domestic airlines — 239 — or 7% of its schedule.

SkyWest, a regional carrier that operates flights under the name American Eagle, canceled 200 flights Sunday. United Airlines canceled 180 flights.

Among international carriers, China Eastern scrubbed 298 flights or 15% of its total schedule and Air China canceled 179 flights, 14% of its schedule, according to FlightAware.

Denver was the hardest hit domestic airport Sunday; 14% of inbound flights to the Mile High City were canceled, and 13% of outbound flights.

Travel experts say passengers should expect to see delays and cancelations for at least another couple of weeks.

“I don’t think you’re gonna see a big drop in cancellation, unfortunately, for the next month as the sort of omicron variant wave peaks and then hopefully recedes quickly,” said travel expert Clint Henderson. “I’m not sure I would tell consumers or leisure travelers to cancel their trip. I would tell folks who have trips planned to have a backup plan.”

David Slotnick, a senior transportation reporter for Business Insider, told NewsNation Prime on Sunday that the flight disruptions will mirror the COVID-19 pandemic as the highly contagious omicron variant makes its way around the country.

“I suspect that as we see it spread across the country, we’re just going to see delays, staffing shortages ebb and flow,” Slotnick said.