A major winter storm sweeping much of the U.S. was producing heavy snow and ice as it threatened areas from the Central Plains through Mid-Atlantic — leaving tens of millions under weather alerts Sunday.

Brutal cold will open the door for a winter storm to take a somewhat unusual track through the South and create treacherous conditions.

Tens of millions of people were bracing Sunday for a massive winter storm forecast to bring the heaviest snowfall and coldest temperatures in over a decade to parts of the country.