A "bomb cyclone" is forecast to intensify an atmospheric river and bring snow to the northern Sierra Nevada starting on Tuesday, with heavy rain expected along the West Coast. Hector Crespo,

A powerful winter storm brewing near the Pacific Northwest known as a bomb cyclone is dragging an atmospheric river.

An atmospheric river and bomb cyclone are what make this storm so powerful — but what do those terms mean? What is an atmospheric river? Atmospheric rivers are no strangers to the western U.S., especially during the fall and winter months.