Airlines cancellations are set to get even worse. Here's why thousands of flights have been scrapped since Christmas Eve.

• Airlines have cut around 20,000 flights since Christmas Eve, including 3,000 on Thursday.
• JetBlue preemptively canceled 1,280 flights scheduled for up until January 13.

Airlines are continuing to slash flights as rising numbers of staff are infected by the Omicron coronavirus variant and bad weather disrupts parts of the US. It could get even worse as COVID-19 cases continue to rise, affecting the millions of people planning to travel on the New Years weekend.

Around 20,000 flights have been canceled since Christmas Eve, according to figures from the flight-tracking website FlightAware.

More than 3,000 flights were canceled on Thursday, with almost half of these arriving in or departing from the US, and more than 17,000 flights were delayed.

As of Friday morning, more than 2,400 flights scheduled to depart that day had been cut.

And JetBlue has canceled 1,280 flights scheduled for between December 30 and January 13, 2022, in anticipation of continuing staffing issues.

Delta also said it expected to cancel between 200 and 300 flights each day over the New Year weekend.

The Federal Aviation Administration said that cases among air-traffic control employees could lead to flight delays in the coming days.

"Like the rest of the US population, an increased number of FAA employees have tested positive for COVID-19," an FAA spokesperson told Insider on Friday morning. "To maintain safety, traffic volume at some facilities could be reduced, which might result in delays during busy periods."

The spokesperson said that existing delays, however, had largely been due to winter weather and high volumes during the holidays.

Airline staff are catching the coronavirus

Some US airlines have attributed their cancellations to staff members who have caught or been exposed to the coronavirus as cases in the US soar. Omicron has become the dominant coronavirus strain in the US, and studies suggest that the variant is more transmissible than previous variants.

A JetBlue spokesperson told Insider that the airline had seen "a surge in the number of sick calls from Omicron." The airline canceled 179 flights on Thursday, or 17% of its schedule for the day, according to FlightAware data.

Joanna Geraghty, JetBlue's president and chief operating officer, told employees in a memo viewed by Insider that it was trying to cancel flights with the least amount of customer disruption. "I know this is not how we wanted the holidays to go, but it is clear we are not through this pandemic," she said.

SkyWest, which is contracted for some regional flights by Alaska, American, Delta, and United, canceled 277 flights scheduled for Thursday, and Delta canceled 163. A SkyWest spokesperson told Insider that cases of the coronavirus among staff had risen. A Delta spokesperson said the Omicron variant had impacted its schedule.

United canceled 223 or 10% flights scheduled for Thursday. A United spokesperson previously told The Associated Press that Omicron's influence on staffing was unexpected and that it was unclear when operations would return to normal.

Parts of the US have been hit by bad weather

Delta, Alaska, and SkyWest spokespeople told Insider that harsh weather conditions, including heavy snow in Washington state, were also to blame for some of the cancellations.

Alaska has been among the US airlines with the most cancellations. The airline canceled 99 flights scheduled for Thursday, or 13%, 172 flights on Monday, or 24% of its schedule.

A spokesperson told Insider on Monday that severe winter weather in the Pacific North West was having a "significant impact" on its operations, particularly affecting flights to and from Seattle. On Thursday, more than a third of flights to and from the city's airport were canceled, per FlightAware data.

"Crew-related cancellations due to COVID are no longer a factor," the Alaska spokesperson said.

Alaska is "strongly urging" flyers with non-essential travel on all routes scheduled before January 2 to consider changing their travel to a later date. "With more snow expected and limited seats available during an already busy holiday week, we're not able to re-accommodate most guests for at least three days," the airline said in a press release.

Delta is also recommending customers set to arrive in or depart from Chicago, Detroit, Salt Lake City, Seattle and the Central & Southern Rocky Mountain region to consider changing their travel date to avoid weather-related disruptions.

Asian airlines have been canceling flights

The bulk of canceled flights globally were operated by Chinese airlines, including China Eastern, which canceled 487 flights on Thursday. Air China has also canceled hundreds of flights this week.

Xi'an, a city in central China with around 13 million residents, entered a strict lockdown on December 23 amid a sudden surge in coronavirus cases. On Thursday, almost 40% of flights to and from the city's international airport were canceled, per FlightAware data.

The Civil Aviation Administration of China (CAAC) also announced in October that it would cut the number of international passenger flights in and out of China between October 31, 2021, and March 26, 2022, by 21.1% compared with the same period in 2020.

Singapore has also frozen ticket sales for quarantine-free flight lanes previously available for vaccinated customers, and Hong Kong has suspended some flights by Korean Air, Cathay Pacific, Emirates, and Qatar Airways from locations including London, New York, and Dubai, United Arab Emirates after some arrivals tested positive for the virus.