As an atmospheric river is expected to bring heavy rain and mountain snow to California, many are turning to Google to search the term "bomb cyclone." But what is that? In short, it's a rapidly intensifying storm system.

The West Coast is preparing for a long-duration heavy rain event from a bomb cyclone set to form Tuesday.Threat level: The rapidly intensifying storm, taking shape in the northeastern Pacific Ocean, is forecast to direct a strong atmospheric river at southwestern Oregon and Northern California for days on end.

Over a month’s worth of rain, hurricane-force wind gusts and feet of mountain snow are coming to parts of the Pacific Northwest and Northern California.