NEW YORK (AP) — For air travelers, the new year picked up where the old one left off – with lots of frustration.

By late Saturday afternoon on the East Coast, more than 2,600 U.S. flights and nearly 4,600 worldwide had been canceled, according to tracking service FlightAware.

That is the highest single-day U.S. toll yet since just before Christmas, when airlines began blaming staffing shortages on increasing COVID-19 infections among crews. More than 12,000 U.S. flights have been canceled since Dec. 24.

Saturday’s disruptions weren’t just due to the virus, however. Wintry weather made Chicago — where forecasts called for 9 inches (23 centimeters) of snow — 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.

Southwest Airlines suspended operations at both Chicago airports because of the forecast, 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.

Southwest canceled more than 450 flights nationwide, or 13% of its schedule. American Airlines and Delta Air Lines scrubbed more than 200 flights each, and United Airlines canceled more than 150.

SkyWest, a regional carrier that operates flights under the names American Eagle, Delta Connection and United Express, grounded 480 flights, one-fourth of its schedule. A spokesperson blamed weather in Chicago, Denver and Detroit and COVID-19 illnesses.

Among international carriers, China Eastern scrubbed more than 500 flights, or about one-fourth of its total, and Air China canceled more than 200 flights, one-fifth of its schedule, according to FlightAware.

Sunday, when many travelers plan to return home from holiday trips, is shaping up to be difficult, too. More than 1,900 flights, including more than 1,000 in the U.S., had been canceled by late Saturday. A winter storm with heavy snow is expected to march toward the Northeast as a new storm hits the Pacific Northwest, according to the National Weather Service.

Airlines say they are taking steps to reduce cancellations. United is offering to pay pilots triple or more of their usual wages for picking up open flights through most of January. Spirit Airlines reached a deal with the Association of Flight Attendants for double pay for cabin crews through Tuesday, said a union spokeswoman.

When winter weather hit the Pacific Northwest earlier this week, Alaska Airlines urged customers to delay any “non-essential” trips that were planned through this weekend. With full flights over the New Year’s holiday, the airline said it wasn’t sure it could rebook stranded passengers for at least three days.

Airlines hope that extra pay and reduced schedules get them through the holiday crush and into the heart of January, when travel demand usually drops off. The seasonal decline could be sharper than normal this year because most business travelers are still grounded.

Travelers who stuck to the roads instead of the skies faced challenges, too. Transportation officials in the Midwest warned motorists that a mix of rain and snow could make roads slippery and reduce visibility, leading to hazardous driving conditions.