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.

A massive plume of moisture from the Pacific called an atmospheric river will hit the West Coast on Tuesday afternoon and last into Friday.

It's the rapid intensification of a cyclone in a short period of time, and it can happen during powerful storms such as the one northern California and the Pacific Northwest are preparing for this week. But what is a bomb cyclone, why does it happen and ...