Winter weather continues to disrupt holiday travel across the United States on Friday, leaving travelers facing delays and cancellations during one of the busiest times of the year.

More than 5,300 Friday flights have already been canceled as of 7:40 p.m. ET, after nearly 2,700 cancellations on Thursday, according to flight tracking site FlightAware.

Thursday's cancellations represented about 11% of U.S.-based carriers' scheduled flights, according to FlightAware, with nearly half of flights delayed on Thursday.

Cancellations were highest Friday at Seattle-Tacoma International Airport, New York's LaGuardia, Chicago O'Hare, Denver International and Detroit Metro Airport, according to FlightAware data. In Canada, Toronto topped flight cancellations.

In addition to the cancellations, there had been more than 9,100 delays as of 7:40 p.m. ET among the flights still going out.

For Saturday, more than 570 flights have already been canceled. But for Christmas Day, just 10 flights have been canceled so far.

Slammed by wind-whipped snow, Buffalo Niagara International Airport in New York had to shut down flights entirely.

"The Buffalo Airport Airfield has closed due to hazardous weather conditions," and all flights scheduled for the evening have been canceled, according to a tweet from the airport's official Twitter account.

At airports in Cleveland and Grand Rapids, Michigan, more than 70% of the flights have been canceled.

Ground stops

The Federal Aviation Administration posted ground stops Friday morning for flights bound for Charlotte Douglas International Airport in North Carolina, American Airlines' second-largest hub, and Reagan National Airport near Washington, DC, because of deicing.

In the Pacific Northwest, FAA notices showed flights bound to Seattle-Tacoma International Airport and Portland International Airport were also under ground stops Friday morning because of snow and ice.

The FAA says the major air pressure changes associated with this storm will trigger high winds at airports from Boston down to Atlanta.

Airports in Chicago and Denver saw the bulk of cancellations and delays on Thursday. Chicago O'Hare International Airport was logging average delays Thursday of almost three hours due to snow and ice.

Storm has bad timing

An arctic blast and a rapidly intensifying winter storm have come at an unfortunate time for travelers trying to join family and friends for the holidays.

Airlines have issued winter weather waivers allowing passengers to rebook at no cost within a limited time period.

The growing cancellations make it harder for passengers racing against the clock and weather to rebook and arrive in time for Christmas. Flights this year were already more crowded than they've been previously — even before the storm disrupted travel schedules.

"We hear about how travel volume is still down, 5 or 10 percent, but what many folks might not have realized is that the number of flights in the sky is actually down more like 15 or 20 percent," Scott Keyes of Scott's Cheap Flights told CNN.

"The planes that are actually flying are more full today than they were pre-pandemic. That's why there's not as many empty seats to switch onto if you do find your flight gets canceled or delayed," Keyes said.

Here are links to major airlines' waivers that allow rebooking without penalty during a short window:

Train and bus service hit, too

Amtrak has also been forced to delay or cancel passenger service for some lines in the Midwest and Northeast.

Click here for details about rail service disruptions.

In its notice, Amtrak said "customers with reservations on trains that are being modified will typically be accommodated on trains with similar departure times or another day.

"Amtrak will waive additional charges for customers looking to change their reservation during the modified schedule by calling our reservation center at 1-800-USA-RAIL."

Meanwhile Greyhound, the largest provider of intercity bus service, issued a service alert Thursday evening indicating that trips in the Midwest or upper Northeast may be canceled or disrupted.

In its alert posted here, the company lists nearly 20 cities as among those impacted. It advised passengers to check bustracker.greyhound.com for the latest information about specific journeys.

Greyhound said riders can call 1-833-233-8507 to reschedule.

Winter weather is also impacting the services of regional intercity bus company Jefferson Lines, which operates in 14 states.

In an alert posted on its website, the company nearly 30 routes have been canceled for Friday, with a few cancellations listed on Saturday and Sunday. Cities impacted by the cancellations include Milwaukee, Minneapolis, Duluth and Kansas City.

Affected travelers can consult the Bus Tracker or call 1-858-800-8898.

A winter storm moving into the mid-Atlantic combined with the pandemic to continue frustrating air travelers whose return flights home from the holidays were canceled or delayed in the first few days of the new year.

More than 1,900 U.S. flights and more than 3,300 worldwide were grounded as of early Monday, according to tracking service FlightAware.

That follows Sunday's cancellations of more than 2,600 U.S. flights and more than 4,400 worldwide. And on Saturday there were more than 2,700 U.S. flights canceled and more than 4,700 worldwide.

A winter storm is expected to bring as much as 10 inches of snow for the District of Columbia, northern Virginia and central Maryland through Monday afternoon.

The cancellations, coupled with more than 5,000 flight delays on Monday, just add to the despair felt over the weekend by holidays travelers trying to get home.

"It was absolute mayhem," said Natasha Enos, who spent a sleepless Saturday night and Sunday morning at Denver International Airport during what was supposed to be a short layover on a cross-country trip from Washington to San Francisco.

Saturday's single-day U.S. toll of grounded flights was the highest since just before Christmas when airlines began blaming staffing shortages on increasing COVID-19 infections among crews.

A winter storm that hit the Midwest on Saturday made Chicago the worst place in the country for travelers throughout the weekend. About a quarter of all flights at O'Hare Airport were canceled Sunday.

Denver's airport also faced significant disruptions. Enos, who was flying on Frontier Airlines, didn't learn that her connecting flight home to California was canceled until she had already landed in Denver. Then it was a rush to find alternative flights and navigate through baggage claims packed with stranded and confused travelers, amid concerns about the spread of the highly transmissible omicron variant of COVID-19.

"It was a lot of people in a very small space and not everybody was masking," said the 28-year-old financial analyst. "There were a lot of exhausted kids and some families were so stressed out."

In Michigan, the authority that runs Detroit International Airport said crews were working around the clock to remove snow and maintain the airfield. Atlanta's airport authority advised travelers to arrive earlier than usual because of high passenger volume, potential weather issues and pandemic-fueled staffing shortages that could lengthen the time it takes to get through security gates.

And thousands of miles from the closest snowstorms, Hawaiian Airlines said it had to cancel several flights between islands and across the Pacific due to staffing shortages.

Southwest Airlines said it was working to help customers affected by about 400 flights canceled around the country Sunday, about 11% of its schedule. The Dallas-based airline anticipates even more operational challenges to come as the storm system pushes into the Eastern seaboard.

Delta Air Lines said Sunday it was issuing a travel waiver for planned flights this week out of mid-Atlantic airports in Baltimore and Washington in preparation for forecasted winter weather.

American Airlines said most of Sunday's canceled flights had been canceled ahead of time to avoid last-minute disruptions at the airport.

SkyWest, a regional carrier that operates flights under the names American Eagle, Delta Connection and United Express, grounded more than 500 flights Sunday, about 20% of its schedule, according to FlightAware.

Airlines have said they are taking steps to reduce cancellations caused by workers affected by the pandemic. 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, a union spokesperson said.

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.

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AP Airlines Writer David Koenig contributed to this report.

HEBRON, Ky. — CVG Airport officials expect Sunday will be one of the airport’s busiest days during the holiday travel period.

WCPO crews saw long lines at airline check-in counters around 5 and 6 a.m.

Flight cancellations are still impacting travelers with thousands of flights canceled across the country. In the last 24 hours, CVG Airport has seen 25 flight cancellations, according to tracking website FlightAware. Cancellations have been caused by winter weather and staffing shortages due to COVID-19 cases.

Overall, travel is up this year compared to last.

“We do expect to serve about 90% of the volume that we saw pre pandemic, so in 2019,” said CVG spokeswoman Mindy Kershner. “We're not quite there yet to normal levels of volume, but we're getting close.”

CVG officials urge travelers to track their flight status online to stay in the loop on delays and closures. Kershner also recommends arriving to the airport early, about two hours before your flight is scheduled to take off.

For drivers, AAA says the worst traffic on the roads will be between 2 and 6 p.m. AAA says drivers will experience the least traffic before 1 p.m.