A massive storm moving across the Midwest has spurred hundreds of flight cancellations across the U.S. on what’s considered “the busiest travel day of the year,” according to Bloomberg and other reports. The storm, which is traveling over the Central Plains toward the Great Lakes, also prompted Kansas Gov. Jeff Colyer to declare a “State of Disaster Emergency” amid reports of motorists stuck in their cars on snowy roads. Some stranded travelers were even spotted leaving their cars and walking through the storm, NBC affiliate KSNW reports. While the National Weather Service predicts the storm will largely weaken by Monday morning, it will nonetheless bring “blizzard-like conditions” such as high winds and up to 10 inches of snow before subsiding, Bloomberg says. More than 200 flights due to land in Chicago’s two main airports, as well as Kansas City, were canceled. A total of 550 flights across the nation were canceled by Sunday afternoon, Bloomberg reports.