By Sharon Bernstein and Steve Gorman
SACRAMENTO, Calif. (Reuters) -Emergency crews braced for the latest bout of high winds and torrential rains sweeping California on Wednesday, renewing the threat of power outages and deadly flooding that gripped parts of San Francisco Bay and Sacramento over New Year's weekend.
The "atmospheric river" - an airborne current of dense moisture flowing from the ocean - was expected to drench much of California ahead of a storm front bringing additional showers to low-lying areas and more snow to the Sierra Nevada Mountains through Thursday.
The incoming blast of extreme winter weather - the next in a succession of storms expected to wash over California in the coming weeks - originated from a sprawling, hurricane-force low pressure system churning over the eastern Pacific, forecasters said.
The National Weather Service (NWS) predicted widespread rainfall totals of 3 to 6 inches, with up to 3 feet of fresh snow in Sierras.
Authorities warned the heavy downpours would likely unleash flash flooding and mudslides, especially in areas where the ground remains saturated from rains that soaked northern California days earlier. Fire-ravaged hill slopes are also particularly vulnerable to slides.
High-wind warnings were posted along the central California coast north through the Bay area and into extreme northern California and Oregon. The National Weather Service (NWS) said gale-force gusts were expected to uproot trees, shear off limbs and knock down power lines, disrupting electricity service in many areas.
San Francisco's transit agency halted its famed cable car service through Thursday due to inclement weather, and scores of commercial flights were canceled at San Francisco International Airport.
Stormy weather was blamed for at least one traffic death in the north Bay city of Fairfield, where pooled water on a roadway sent a car crashing into a utility pole, killing the driver, the San Francisco Chronicle reported.
Voluntary evacuation notices were issued for homes along three roads in a flood-prone area of Alameda County, across the bay from San Francisco, citing threats posed by "the impending storms, saturated soils and current runoff."
Governor Gavin Newsom declared a state of emergency on Wednesday to support the state's winter weather hazards response, and activated California's flood operations center.
The governor's Office of Emergency Services said it had staged crews in several northern counties likely to be hardest hit by flooding, and where previous wildfires have stripped hillsides of vegetation, leaving them at high risk of mudslides.
State Natural Resources Secretary Wade Crowfoot urged residents in such areas to stay indoors unless ordered to evacuate, and to prepare for power outages by charging electrical devices and having flashlights and candles handy.
Sacramento County crews were still out on Wednesday repairing levee breaches along the Cosumnes River, near Sacramento, where flooding last weekend closed Highway 99, Crowfoot said at a news briefing in the state capital.
At least three deaths have been attributed to last weekend's storm. Two bodies were recovered from Cosumnes River flood zone, and a 72-year-old man was found dead under a fallen tree in Santa Cruz, authorities said.
The latest round of extreme weather was the second in a series of potentially damaging storms expected to hit the state over the next seven to 10 days, Nancy Ward, director of emergency services, told reporters. The state operations center had been placed at its highest level, she said.
“We anticipate that this may be one of the most challenging and impactful series of storms to touch down in California in the last five years,” she said.
Fallen trees, already weakened by prolonged drought and now left poorly anchored in rain-soaked soil, were likely to pose a significant hazard in the upcoming storms, said Karla Nemeth, director of the state Department of Water Resources.
She said coastal areas from Los Angeles north to Crescent City near the Oregon border faced the greatest flood potential, especially, especially in Mendocino County along the Russian and Navarro rivers.
Nemeth said the increasing frequency and intensity of episodic floods punctuating California's multi-year droughts are symptomatic of extreme swings between wet and dry wrought by climate change.
The good news was that recent storms have left the Sierra snowpack, a major source of California's water supplies, at well above average for this time of year, though far more will need to accumulate through winter to end the drought, experts say.
(Reporting by Sharon Bernstein in Sacramento, Calif.; Writing and additional reporting by Steve Gorman in Los Angeles; Editing by Josie Kao, Grant McCool and Michael Perry)