A so-called "atmospheric river of rain" began falling on Northern California on Friday, bringing worries about flash floods, high winds and mudslides but offering little relief to a state that has been left parched by several years of drought.
The storm, also known as a "Pineapple Express" because it develops from a ribbon of moist air moving across the Pacific Ocean, was forecast to dump as much as 10 inches (25 cm) of rain in coastal mountains.
National Weather Service meteorologist Austin Cross said more than three inches (7.5 cm) of rain had been already recorded in the hills of western Sonoma County by early Friday afternoon.