The storm, one of two predicted for the weekend, hit the Bay Area before dawn and knocked out power to about 1.2 million people from Central California to the Oregon border. With repair crews in some areas forced to retreat in the face of flying debris and tree limbs, Pacific Gas and Electric, Northern California’s chief utility, warned that some customers could be without electricity through the weekend.
Forecasters promised punishing conditions for Southern California as well. Extremely heavy rain was expected there, raising the prospect of mudslides, particularly in areas stripped of vegetation by the wildfires of 2007. In expectation of such slides, The Associated Press reported, officials late Friday ordered the mandatory evacuation of about 1,000 homes in four Orange County canyons.
Here to the north, conditions were already challenging. Several major Bay Area roads, including Highway 101 and Interstate 580, were closed for much of the day by airborne construction materials and overturned vehicles, including five trucks that flipped on the Richmond-San Rafael Bridge, a major east-west thoroughfare spanning a northern finger of San Francisco Bay.
A downed tree on the tracks stopped BART rail service in the Mission District of San Francisco, sending evacuated passengers into the rain or onto buses. Morning ferry services across the bay were canceled as docked boats rocked like rubber ducks in a bath.
Scaffolding collapsed, breaking windows, taking down power lines and bringing electrically powered buses to a halt along at least one major San Francisco boulevard. People trying to make it to work dodged flying trash cans, orphaned umbrellas and dislocated newspaper vending machines.
Dozens of flights were canceled at the San Francisco airport, where winds topped 65 miles an hour at midmorning, making for even more flight delays than cancellations. Harrowing whitecaps from the bay lapped at the foot of the runways.
The most extreme conditions were about 200 miles to the east of San Francisco, in the Sierra Nevada, where the National Weather Service warned of blizzard and whiteout conditions and gusts of 160 miles per hour. Just hours into the storm, a 163-m.p.h. gust was reported on one mountaintop near Lake Tahoe.
Power was sporadic in some mountain towns along Interstate 80 from Sacramento to Reno, Nev. Only the hardiest of trucks and tire-chained cars were crawling along that stretch Friday.
Forecasters said trying to travel through the storm would be foolhardy.
“It’s an exceptional storm,” said Rhett Milne, a Reno meteorologist with the Weather Service. “If you do get stranded, it’s a life-threatening situation.”
The Weather Service said some upper elevations could get up to 10 feet of snow by the time the twin storms blow through at weekend’s close, and some ski resorts, visibility eliminated by blowing snow, had already shut their high-mountain lifts.
Even in less exposed areas, daily routines were brought to a halt by wind and rain. In San Anselmo, a pleasant commuter town north of San Francisco, shops were closed, floodgates were in use, and merchandise was moved to higher shelves. A New Year’s Eve flood two years ago badly damaged some local businesses there, and sandbagging for this storm started Thursday night, said Lauren Gregory, an owner of Bloomworks, a flower shop.
“It was really, really difficult for businesses to recover,” Ms. Gregory said of the earlier flood’s aftermath. “Most did, but they still haven’t really caught up financially and gotten out of debt. To go through that again would really be devastating.”
Forecasters attributed the storm to a particularly violent collision of subtropical moisture and a blast of arctic air, and the same system also lashed areas farther north. At the Washington-Oregon border, the ocean entrance to the Columbia River was closed to ship traffic, as was the entrance to Tillamook Bay, in northwest Oregon, the Coast Guard said. Inland, the police closed stretches of Interstate 84 for several hours after high winds toppled tractor-trailers.
In Washington, where December storms caused six deaths, meteorologists warned of more snow in the Cascade Mountains. Winds and unstable snow there would make conditions treacherous. Eight fatalities have already been attributed to avalanches in the state this fall and winter, making this the deadliest avalanche season in three decades, and forecasters weighed Friday whether to issue another avalanche warning.
After several consecutive dry years, not everyone in California was unhappy about Friday’s storm. Hydrologists at the California Department of Water Resources said five inches of rain had already fallen in reservoirs in northern counties, and were hopeful that the storm might single-handedly make up for a dry November and below-average rainfall last month.
And in parts of the ski-happy Sierras, where forecasters said snow could fall at a rate of several inches an hour for most of the weekend, resort operators were dreaming of a thick powder unlike any seen in the last couple of winters.
“We’re always pretty well equipped for the weather — that’s why we love living here,” said Roy Moyer, general manager of the Tamarack Lodge and Resort, a cross-country center near Mammoth Lakes, Calif. “So bring it on.”
Which the storm was busy doing. By midafternoon, some two feet of snow had fallen at Mammoth Lakes.