Heavy snow and ice led to thousands of flight cancellations across the country as the ripple effects of the storm trickled through the airline networks. Airlines cancelled nearly half of all flights into and out of Atlanta on Friday, according to airline tracking company FlightAware. Atlanta is home to the world’s busiest commercial airport.

A powerful winter storm brought heavy snow and icy conditions to parts of the U.S. South on Thursday, forcing officials to close schools, cancel flights and warn residents in some of the worst-hit areas to stay off roads as it lumbered eastward through Oklahoma and Texas.

Another blast of winter storms is closing schools, snarling flights and putting millions of residents on alert across parts of the Deep South and south-central U.S. The National Weather Service says heavy snowfall and icy conditions are likely Friday in Mississippi,