More than 100 million Americans are under alerts for snow, ice and flooding as three winter storms cross the country over the next few days. The first storm is bringing heavy snow to parts of West Virginia, Virginia and Maryland.

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.