Winter Storm Enzo was not your typical winter storm, but its rain and snow were caused by a classic setup. Enzo never truly had a robust low pressure system, but instead was a large overlap between the coldest air of the season, abundant moisture and the tail end of a deep upper-level trough.

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.

A historic winter storm swept across the Gulf Coast on Tuesday, bringing heavy snow and icy conditions to the Southeast while most of the country was facing dangerously cold temperatures from an arctic blast that arrived over the weekend.