Airlines canceled nearly 2,000 U.S. flights as of Saturday morning following a massive winter storm that snarled airport operations around the United States and frustrated thousands of holiday travelers.

Total flight delays within, into or out of the United States amounted to about 4,000 as of Saturday morning, according to flight tracking website FlightAware, which showed that total U.S. flight cancellations stood at around 2,000. The flight cancellations on Saturday morning included over 450 from Southwest Airlines (LUV.N) and nearly 400 from Delta Air Lines Inc (DAL.N).

The flight disruptions came as an arctic blast gripped much of the United States on Saturday, causing power outages and car wrecks. Plummeting temperatures were predicted to bring the coldest Christmas Eve on record to several cities from Pennsylvania to Georgia.

Temperatures are forecast to top out on Saturday at just 7 degrees Fahrenheit (minus 13 Celsius) in Pittsburgh, surpassing its previous all-time coldest Christmas Eve high of 13 F, set in 1983, the National Weather Service (NWS) said.

Winter storms have increased in frequency and intensity over the past 70 years, according to the U.S. Global Change Research Program. This is in part due to climate change, according to the Environmental Defense Fund, because the planet evaporates more water into the atmosphere as it warms, leading to more overall precipitation.

On Friday, U.S. flight cancellations stood at 5,936, according to FlightAware.

“Increased air traffic volume and winter weather affecting the Northern half of the U.S. could still cause delays to holiday travel,” the Federal Aviation Administration (FAA) said on Saturday, though travel conditions were expected to improve.

An NBC News affiliate reported that inclement weather canceled over 130 flights as of Saturday morning at the Seattle-Tacoma International Airport. Some passengers there told the news outlet they were not notified before coming to the airport.

An ABC News affiliate showed long lines at the Denver International Airport on Saturday morning, where over 150 flights were delayed and nearly 130 were canceled.

Passenger railroad Amtrak also canceled dozens of trains through Christmas, disrupting holiday travel for thousands.