Millions of Californians are under threat from an approaching storm that could trigger intense downpours and widespread flooding in many parts of the state, including in some mountainous areas already buried under a near-record snowfall.

After a weeks of unusually bad weather on the West Coast, another storm known as an atmospheric river could dump as much as 3 inches of rain in the San Francisco Bay area and across the Central Coast through the weekend, the National Weather Service said in its forecast.