A few thousand customers in Oregon were without power as well.
Parts of Washington experienced strong wind gusts, including Everett, about 25 miles north of Seattle, where gusts of up to 61 m.p.h. were recorded, according to the National Weather Service in Seattle.
“The atmospheric river is aiming a fire hose, if you will, into our area,” Sean Miller, a meteorologist for the Weather Service in Monterey, Calif., the forecast office for the Bay Area, said on Sunday.
An atmospheric river is a concentrated plume of moisture that extends over the ocean, typically in the troposphere, the lowest layer of the atmosphere, Mr. Miller said. The current trough was angled toward the North Bay, he said.
In the Pacific Northwest, a bomb cyclone, a type of storm known for its falling atmospheric pressure, was expected to push the atmospheric river south, affecting areas south of San Francisco, Mr. Miller said.
“This is more typical of something we tend to see in December or January,” he said, pointing out that the confluence of the two meteorological phenomena was “anomalous.”
Throughout the day, the San Francisco Fire Department posted updates on Twitter about flooding, felled trees, fires, and stalled vehicles on flooded roadways. On Monday the department said it rescued two adults who had become trapped in a car after driving into water along Hunters Point Expressway. One of them received medical care.