SAN FRANCISCO â€” Authorities urged thousands of people in Northern California to evacuate homes as rivers swollen by four days of heavy rain threatened to crest above flood level, even as another day of showers was forecast for Wednesday.
About 2,000 people in Wilton, a rural California community near Sacramento, were asked to leave their homes Tuesday evening, as emergency crews and officials worked to try to bolster a Cosumnes River levee in Sacramento County. The river was projected to overflow its banks Wednesday morning.
Sacramento County emergency services official Mary Jo Flynn said water was expected to start spill over the levee, flooding low-lying roads and buildings with up to 1 foot of water.
Flynn pointed out many of the homes along the path of a possible flood are built on berms or sit on relatively higher ground.
An evacuation centre opened Tuesday evening in neighbouring Elk Grove but some residents said they plan to stay put.
"We have no concerns," Lill Nichols, who with her husband runs a horse farm near the river, told the Sacramento Bee. "We have animals and can't evacuate anyway."
Some 3,000 Sonoma County residents were under an evacuation advisory as the Russian River rose again under pounding rain. Officials red-tagged seven homes, ordering residents out, when a rain-soaked embankment came crashing down.
Johna Peterson was one of few residents who ventured out in the remote Sonoma County town of Monte Rio. Walking on the bridge across the Russian River, Peterson worried about what the coming hours and days would bring.
"I think it's going to go higher," Peterson said. "There's nowhere for this water to go."
In nearby Forestville, Kathy Granados huddled with two other people under an awning at the River Bend RV Park, watching the downpour.
"We're waiting it out," she said. "Yesterday the water dropped, but it's going to get higher. We're just sitting here. We have no electricity, no heat."
North of San Francisco, people were evacuated Tuesday evening from businesses and homes in downtown San Anselmo after a rain-swollen creek broke its banks. The Corte Madera Creek was flowing 1 foot over flood stage, the Marin County Sheriff's Office said.
Tuesday's storm was the latest of back-to-back systems â€” buffered by a brief respite Monday â€” that have brought the heaviest rain in a decade to parts of Northern California and Nevada. More showers were forecast for Wednesday morning.
The storms are part of an "atmospheric river" weather phenomenon that draws precipitation from the Pacific Ocean as far west as Hawaii. Its impact can be catastrophic.
A blizzard warning was in effect for parts of the Sierra Nevada, the first issued in the past nine years, said Scott McGuire, a forecaster for the National Weather Service based in Reno, Nevada.
"This is definitely a dangerous, life-threatening situation going on up there," he said. "People should not attempt to travel at all."
Forecasters warned of up to 10 feet of snow in the highest mountains, with up to 7 feet of snow around the resorts of Lake Tahoe, high risk of avalanches, and wind gusts to 60 mph. The Sierra ridge had gusts of more than 100 mph.
Many ski resorts shut down Tuesday because of the storm. A number of main roads in the Sierra were closed, including Interstate 80, or required chains.
Nearly 3 feet of new snow already was reported Tuesday morning at the top of the Mount Rose ski resort between Reno and Lake Tahoe. A series of storms already has added 33 billion gallons of water to Lake Tahoe since Jan. 1.
Risberg reported from Guerneville. Associated Press writers Ellen Knickmeyer, Olga R. Rodriguez, and Jocelyn Gecker in San Francisco, and Scott Sonner in Reno also contributed to this report.
Eric Risberg And Janie Har, The Associated Press