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.

Snow, freezing rain and rain are underway in the southern Plains as a potent winter storm strengthens Thursday.

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 storm started dumping a mix of sleet and heavy snow Thursday morning in north Texas and Oklahoma,