Airlines may have thought their pandemic woes were over in the fall, when a coronavirus wave passed and more people took to the skies. However, a new virus outbreak and winter storms have left the airlines and their passengers in a holiday bind.

Airlines have been canceling over 1,000 flights per day to, from, or within the United States as we approach the New Year’s weekend, when return flights will cause another surge in air travel. On Friday, more than 1,200 flights were canceled. Carriers and employees say the latest chapter of the pandemic, the Omicron variant, has severely limited their ability to staff flights, despite the fact that the vast majority of crew members have been vaccinated.

According to the air travel data site FlightAware, JetBlue was one of the hardest hit airlines, canceling 17% of its flights on Thursday. The airline announced on Wednesday that it would cut approximately 1,280 flights through mid-January, citing an increase in virus cases in the Northeast, where its operations and crews are concentrated.

The next few days could be just as aggravating. According to Dan DePodwin, director of forecast operations at AccuWeather, storms in Southern California and the Northwest could combine to dump snow on airline hubs in Denver and Chicago, with severe thunderstorms also threatening Dallas Fort Worth International Airport.

Alaska Airlines, whose main hub is Seattle-Tacoma International Airport, has gone so far as to advise passengers to postpone non-essential travel until the end of the year. As more snow fell in Seattle on Thursday, 14 percent of the airline’s flights were canceled.

According to Transportation Security Administration estimates, up to 10 million people may fly from Thursday to Monday. Airlines have been preparing reserves of workers for the holiday rush for months. However, in a rapidly changing situation, those measures were insufficient, and many passengers were dissatisfied.

Airlines began hiring again this year as the travel rebound took off, but most have yet to fully restore their work forces: According to federal data, the industry employed nearly 413,000 people in October, a decrease of nearly 9% from the same month in 2019. Airlines have struggled to make a profit as passenger volumes remain about 15% below pre-pandemic levels.

In recent days, the industry has looked to the Centers for Disease Control and Prevention for a partial solution to its staffing issues, lobbying for a reduction in the 10-day isolation period recommended for those infected with the coronavirus to five days. Unaffiliated with airlines, some scientists proposed a similar solution to bolster overworked workforces in other industries, such as hospitals.

The C.D.C. changed its advice on Monday to five days of isolation followed by five days wearing a mask for people whose symptoms have ended or are abating. The change was motivated by findings that the coronavirus was mostly transmitted one to two days before symptoms appeared and two to three days afterward, according to the agency.

Delta is offering infected employees five days of sick leave, plus two additional paid sick days if they choose to be tested on Day 5 and the results are positive.

The industry is divided over the shorter isolation time. In a letter to airlines on Tuesday, the Association of Flight Attendants-CWA, which represents nearly 50,000 flight attendants at 17 airlines, urged airlines to maintain a 10-day isolation period.

Airlines always prepare for chaos, especially around the holidays, when bad winter weather in one location can throw an entire system off-kilter. However, the industry has been particularly hard hit this year.

After two airlines, American and Southwest, canceled thousands of flights in October due to severe weather and a temporary shortage of air traffic controllers, they vowed to address the issues by offering bonuses to encourage employees to work throughout the holiday season, increasing hiring, and pruning flight plans. This holiday season, both have avoided widespread cancellations.

According to Constance von Muehlen, Alaska Airlines’ chief operating officer, the airline spent months planning for the holiday season, investing in staff and equipment to deal with winter weather and lining up backup flight crews.

The airline managed the high number of sick calls by offering extra pay for others to fill in, but sustained snowfall and record low temperatures in the Seattle area forced it to cancel nearly one-third of its flights on Sunday, about one-quarter on Monday and about one-fifth on Tuesday.