Airlines canceled more than 2,500 U.S. flights on New Year's Day, many of them into or out of the storm-battered Upper Midwest, as wintry weather and staffing shortages amid a spike in coronavirus cases made Saturday the worst of several straight chaotic days for air travelers.

As of early Saturday evening, 2,627 flights within, into or out of the United States had been canceled, easily the highest daily total in more than a week of havoc for airlines, according to FlightAware, which compiles commercial aviation data.

Twenty-seven flights out of Reagan National and 22 into the airport had been canceled as of early Saturday night. Cancellations at Dulles International were 20 flights out and 19 inbound.

In snowy Chicago, 408 flights out of O'Hare International Airport and 129 out of Midway International were scrubbed, making the Windy City the hub of air travel disruptions nationwide, FlightAware data showed. In addition, as night fell Saturday, nearly 600 flights into those two airports had been canceled.

Among major U.S. carriers, Southwest Airlines was the hardest hit, with 473 flights grounded, or about 13% of its schedule, according to FlightAware. Amid high winds and whipping snow in Chicago, Southwest halted operations at both of the city's airports.

Across the country, there had been concerns about whether carriers could cope with passenger volumes during the busy holidays after high-profile breakdowns over the summer and fall. Airlines passed their first major test over Thanksgiving. But Christmas, and now New Year's, have been a different story, with thousands of travelers stranded.

SkyWest Airlines had canceled 472 flights as of early Saturday evening, American Airlines had canceled 208 flights, Delta Air Lines 200 and United Airlines 158, according to FlightAware.

"Weather and heavy seasonal traffic are likely to result in some travel delays in the coming days," the Federal Aviation Administration had warned in a statement before the weekend, adding that it, too, was coping with staffing shortages. "Like the rest of the U.S. population, an increased number of FAA employees have tested positive for COVID-19."