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, where schools canceled classes for more than 1 million students.

An area stretching from Texas to Tennessee is bracing for the expected arrival of freezing rain and snow, as some other parts of the country that already received an arctic blast this week are preparing to go another round with the plunging polar vortex.