Even if you haven’t had to fly anywhere yesterday or today, you’re likely aware that there’s a large storm system currently duffing up air travel across the U.S. Time to break out the leftover egg nog and reconcile yourself to the inevitable nog hangover, travelers, as thousands of flights have been canceled or delayed already.

As of Monday afternoon, more than 1,807 flights into, out of or within the U.S. have been canceled, while a further 2,973 have been delayed, according to flight-tracking service FlightAware. On a typical day, usually about 150 flights are canceled and 4,000 delayed.

Almost half of those cancelations have been in Chicago, at both O’Hare International Airport and Midway, while Dallas-Fort Worth International Airport was also hit especially hard. Denver, Detroit, Milwaukee, Kansas City, St. Louis, Oklahoma City, and Lubbock, Texas haven’t had a great time of it lately, either.

A large storm system moving through the country is largely responsible, bringing tornadoes to Texas and heavy rains and strong winds to Missouri, Illinois and Arkansas.

Even if you personally are not flying to or from the areas covered by the storm system, mass delays and cancellations tend to have a ripple effect through the entire air traffic system. Before you head to the airport, it’s a good idea to check your flight’s status online or call the airline. Rebooking will likely be difficult, so be prepared to wait a day (or even two) before you can get on a plane.

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