What are atmospheric rivers and bomb cyclones?

Atmospheric rivers are storms akin to rivers in the sky that dump massive amounts of rain and can cause flooding, trigger mudslides and result in loss of life and enormous property damage. One such storm — along with a bomb cyclone — was battering California on Thursday, killing a child and knocking out power to tens of thousands.
Atmospheric rivers can carry up to 15 times the volume of the Mississippi River, according to the National Oceanic and Atmospheric Administration. They appear as a trail of wispy clouds that can stretch up to hundreds of miles.

This is the third atmospheric river storm, and the strongest, to hit California since last week, according to meteorologist Bob Oravec of the National Weather Service.