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.

The Tennessee Valley could see some of the heaviest snowfall, with 6 inches expected on Friday. A wide swath of the country is under winter weather warnings and advisories and will see impacts including "widespread closures, treacherous travel, scattered power outages, and downed branches," the weather service said.