More than 2,500 flights cancelled in the U.S. due to bad weather

More than 2,500 flights have been canceled in the United States, according to flight-tracking site FlightAware, as severe winter weather threatens vacation travel.

Chicago O’Hare International Airport leads the cancellations, followed by Denver International Airport and Chicago Midway International Airport. Cancellations at those airports could have a broader impact, as they are busy hubs where travelers often change planes to reach other destinations, CNN reported.

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Meteorologists are forecasting a “cyclone bomb,” and the National Weather Service says more than 100 million people are under warnings, that’s about one-third of the U.S. population.

Many airlines have issued travel easements because of the bad weather, and travelers should check to make sure their flights are still scheduled to take off before leaving for the airport. Experts warn travelers to arrive early at the airport to avoid crowds.