A rare frigid storm charged through Texas and the northern Gulf Coast on Tuesday, blanketing New Orleans and Houston with snow that closed highways, grounded nearly all flights and canceled school for more than a million students more used to hurricane dismissals than snow days.

Around 40 million people in the U.S. are under a winter storm warning from an unusual blast of severe cold weather and snow across the South.

Heavy snow, sleet and ice are making travel conditions treacherous across the region, stretching from Houston into the Florida panhandle.