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.

Meanwhile, Southern California this week will see dry conditions amid gusty Santa Ana winds that could raise the risk of wildfires in areas where crews are still mopping up a major blaze that destroyed 240 structures.