Snow and icy conditions threatened to paralyze parts of the U.S. South from Texas to Alabama on Thursday, as officials closed schools, canceled or delayed flights and warned residents in some of the worst-hit areas to stay off roads as a winter storm moves east.

A powerful winter storm that dumped heavy snow and glazed roads with ice across much of Texas and Oklahoma lumbered eastward into southern U.S. states overnight, prompting governors to declare states of emergency and shuttering schools across the region.