Marin absorbs first major rain storm of season

An “atmospheric river” storm blasted Marin County with steady rain and stiff winds Wednesday as a prolonged stretch of wet weather swept into the region.

“This is really our first big storm of the season,” said Rachel Kennedy, a meteorologist with the National Weather Service. “It is really kicking the season off with a bang.”

The agency reported about 2 inches of rain in Novato and San Rafael, 2.46 inches in Point Reyes Station, 1.84 inches on Mount Tamalpais, 0.9 inches in Mill Valley and 0.71 inches in Sausalito.

Forecasters expect Marin to receive 3 to 5 inches of rain between Wednesday and Saturday, Kennedy said, and possibly up to 6 inches on Mount Tamalpais. The weather system is expected to ease slightly on Thursday, with lighter showers forecasted.

A new storm will arrive Friday night into Saturday morning, bringing moderate to heavy rainfall, Kennedy said.

“That will be the second punch of our rainy week,” she said.

Rain is expected to linger until at least Tuesday.

“I’d rather have smaller systems spread out over five days than all of it in one day,” said Jan Null, a meteorologist with Golden Gate Weather Services in Half Moon Bay. “It causes less mayhem.”

The National Weather Service issued a flood watch through 4 a.m. Saturday for Marin, Sonoma and Napa counties, as well as a high surf advisory from Big Sur to the Sonoma Coast, with large breaking waves 14 to 22 feet high expected.

Gusts are expected to reach 50 mph to 55 mph on Wednesday. At higher elevations, gusts were expected to go as high as 60 mph.

“As we start to see rain shift a little further south, especially in Marin County, we may start to see more nuisance flooding,” Kennedy said. “Roads and transportation are expected to be impacted.”

California Highway Patrol Officer Darrel Horner said crews handled an increase in storm-related traffic incidents Wednesday, mostly spinouts.

The Marin County Fire Department received about 40 reports of fallen trees and downed power lines on Wednesday, said spokesperson Marimar Ochoa. No significant injuries were reported.

Battalion Chief Jeff Whittet of the Novato Fire Protection District said the agency received reports of downed power lines, but no major injuries.

Pacific Gas & Electric Co. had approximately 10,000 customers without power in Marin by about 2:30 p.m., but the number was down to 620 by 6 p.m., said Paul Moreno, a spokesperson for the utility. The outages were largely caused by trees and branches coming into contact with power lines, he said.

Moreno said crews from the South Bay have been assigned to assist in Marin to restore power faster if there are additional outages.

Elsewhere in the Bay Area, San Francisco is expected to receive 2 to 3 inches by Friday night, with Oakland getting 1 to 2 inches and San Jose and Santa Cruz about 1 to 1.5 inches, the National Weather Service said.

The University of California Central Sierra Snow Lab forecast 10 to 20 inches of snow falling along Donner Summit near Lake Tahoe by Friday, just in time for Thanksgiving, the traditional start of ski season. The CHP issued chain controls around noon Wednesday for Interstate 80 between Truckee and Cisco Grove.

Overall, the multiday storm was expected to bring the most rain to the Bay Area of any storm system in roughly 9 months. While its slow start might have been disappointing to some in the drier parts of the Bay Area, that contrasted with rising creeks, flooded storm drains, and downed trees in the North Bay, where wind gusts reached 50 mph at times.

The storm was driven by a “bomb cyclone” off the coast of British Columbia. A large mass of warm moist air from the south collided with a mass of cold air from Alaska. That caused the warm air to rise, and the barometric pressure to fall dramatically, creating an enormous swirling air mass.

That system pulled in an atmospheric river — or long, moisture-rich plume of air from north of Hawaii — to California, bringing the rain.

“Mid-latitude cyclones of course can exist on their own without an atmospheric river and they’re not always big events,” said Daniel Swain, a climate researcher at the University of California, Los Angeles. “But it is when these two things occur together that we tend to get our biggest, most dramatic storms along the West Coast.”

Bay Area News Group contributed to this report.