An atmospheric river dumping rain across Northern California and several feet of snow in the Sierras was making its way across the state Friday, bringing flooding and threatening mudslides along with it.

In northern California, flood and high wind watches were in effect, with up to 8 inches (20 centimeters) of rain predicted for parts of the San Francisco Bay Area, North Coast and Sacramento Valley.

A bomb cyclone occurs when cold and warm air collide over the ocean, dropping the pressure at a rapid rate and creating intense weather. On the East Coast, that can mean vast quantities of snow. Here on the West Coast, it can usher in buckets of rain.