(NewsNation Now) — The holidays are over, but flight cancellations and delays are continuing into the workweek, causing frustrations for thousands of air travelers.

The TSA predicted Monday would be the busiest travel day of the holiday season and it’s already hectic in many of the nation’s airports.

As of 9 a.m. ET Tuesday, 1,204 U.S. flights and 4,679 worldwide were grounded, according to tracking service FlightAware.

Southwest reported the highest number of cancellations for a U.S.-based airline for the day, canceling 314 flights nationwide, or 10% of its schedule, so far.

SkyWest, a regional carrier that operates flights under the name American Eagle, canceled 151 flights Tuesday. JetBlue canceled 107 and United Airlines canceled 65 flights.

Among international carriers, China Eastern scrubbed more than 743 flights or 34% of its total schedule and Air China canceled more than 198 flights, 16% of its schedule, according to FlightAware.

The Christmas and New Year holidays are typically a peak time for air travel, but the rapid spread of the highly transmissible omicron variant has led to a sharp increase in COVID-19 infections, forcing airlines to cancel flights as pilots and cabin crew quarantine.

Disruptions weren’t just due to the virus, however. Over the weekend, wintry weather overnight made Chicago the worst place in the country for travelers. More than 800 flights were scrubbed at O’Hare Airport and more than 250 at Midway Airport on Saturday into Sunday. O’Hare received just over 4 inches of snow.

Southwest Airlines suspended operations at both Chicago airports because of the snowstorm, according to an airline spokeswoman. She said Southwest knows from years of operating at Midway that high winds and blowing snow make it hard to get planes back in the air quickly.

U.S. health officials halved guidance to five days of quarantine for asymptomatic Americans who catch the coronavirus. Airline industry experts say that will alleviate the staffing issues that have forced airlines to scratch flights — but the flight attendant unions say they’re wary of the change and its effect on worker health.

Getting past the holiday rush will also help. January and February are the year’s slowest travel months after the New Year’s rush, said Willis Orlando, senior flight expert at Scott’s Cheap Flights: “There should be a lot more room for airlines to cut routes, reassign pilots and have staff in reserve.’’