The so-called polar vortex that descended into the U.S. this week has wreaked havoc with airline schedules, according to statistics from industry data tracking service FlightAware. Airlines on Monday canceled 4,590 flights within, into or out of the U.S., while delays totaled 8,064. Chicago O’Hare registered the most cancellations of all the nation’s airports, both for incoming and outbound flights. The airport saw 62 percent of its incoming flights cancelled and 8 percent delayed. Airlines operating out of O’Hare cancelled 65 percent of their outgoing flights and reported delays on another 10 percent.

Regional airline ExpressJet led all airlines in number of cancellations, reporting 603, or 24 percent of its flights systemwide. It also experienced 591 delays.

The bitter temperatures—some of the coldest to have hit the U.S. in 20 years—stretched as far south as Florida, where even Orlando International saw 9 percent of its flights cancelled and 27 percent delayed.

By 2 p.m. on Tuesday, FlightAware statistics showed 2,415 cancellations and 3,398 delays for the day, as weather-related disruptions had spread throughout two-thirds of the country. Again, Chicago O’Hare experienced the most disruptions in terms of numbers of cancellations, but Cleveland Hopkins saw the greatest portion of its flights cancelled at some 50 percent.

“The biggest issue affecting travel this week is weather—[a] perfect storm of snow and ice storms, followed by record extreme cold temperatures, which is rather unprecedented and continues to impact airline operations [e.g., ground service equipment refueling and crew repositioning as airlines begin to recover] at certain locations in the Midwest and Northeast,” an Airlines for America spokesperson told AIN. “U.S. airlines have decades of experience dealing with weather events, such as those we are seeing now and are proactively working to minimize the impact on customers, while also ensuring the safety of airline crew that are in the exposed elements.”