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 an expected snowstorm even as some other parts of the U.S. hit by the plunging polar vortex this week are beginning to shake off its icy effects.