LOS ANGELES — California, already reeling from previous waves of heavy rain and snow, faced another drenching on Tuesday as the latest “atmospheric river” stormed in, wreaking havoc with high winds and flooding that closed roads and schools, knocked out power and prompted evacuations in vulnerable areas.
The storm system, which began to move in from the Pacific late Monday and swept across the state on Tuesday morning, dumped more rain on a landscape already saturated with water. At higher elevations, the storm was piling more feet of snow on top of already groaning roofs, or wetting down the existing snowpack.
The storm was expected to create significant flooding as it spread across the Central Valley and into the Sierra Nevada foothills, the National Weather Service said — a danger that would extend into Wednesday. There could be flooding even in areas that are not normally prone to it, endangering lives and property, the agency said.
The leading edge of the storm came ashore overnight in Northern California, and by late morning on Tuesday had begun to shift the brunt of its impact to the south. Up to four inches of rain was forecast for the Los Angeles Basin, where “extensive street flooding” was likely, the Weather Service said.
Officials up and down the state issued warnings for vulnerable spots. Santa Barbara County told people living near the burn scars of recent wildfires to evacuate, saying those areas could experience dangerous flooding and debris flow. Plumas County, north of Sacramento, warned residents living along the Feather River and in other low-lying areas to be ready to head for higher ground.
In Oceano, a neighborhood under an evacuation warning in San Luis Obispo County, residents said they were worried that a nearby levee, already damaged by storms in January, could fail, as one on the Pajaro River did on Saturday.
“If it does, it will flood here,” Willie Reed, 44, said as sat on his front porch on Tuesday, watching the rain. Mr. Reed said that he and his fiancée had packed their bags and were ready to go. Near his house, ducks swam across a street already inundated with rain.
The American Red Cross has a shelter open in San Luis Obispo for evacuees, but as of noon no one had turned up there except reporters. “We have not had one single person yet,” said Michael Turk, the supervisor of the shelter. People who can stay with family or friends generally will choose to do that, Mr. Turk said, while “we’re here for the people that don’t have options.”
Sections of highways and roads in some parts of the state were closed by rockslides, flooding and downed trees loosened by the wind and rain, the California Department of Transportation said. Officials warned motorists to avoid driving where moving water covered the pavement, noting that “as little as one foot of water can sweep a car off the road.”
Schools were forced to close in a number of communities, especially along the Central Coast.
The storm’s gusty winds — reaching more than 80 miles an hour in some areas — were toppling trees and snapping power lines, causing widespread power outages. As of Tuesday afternoon, roughly 330,000 utility customers were without power in California, according to PowerOutage.us. The winds caused flight delays at San Francisco International Airport, officials said.
The storm is the latest bout of severe weather in what is shaping up as one of the most ferocious California winters in memory. Previous storms have already forced some residents to evacuate from floods and trapped others in their homes beneath mounds of snow.
The southern portion of the Sierra Nevada now has what may be its deepest snowpack on record, according to Daniel Swain, a climate scientist at the University of California, Los Angeles. Scientists say this winter has already been the third snowiest on record for the central Sierra.
Gov. Gavin Newsom declared a state of emergency this month covering several counties that have been ravaged by the recent storms, and President Biden has approved a federal emergency declaration as well.
Katya Cengel contributed reporting from Oceano and San Luis Obispo, Calif.