A so-called atmospheric river of rain and powerful wind triggered massive delays at San Francisco International Airport, knocked down power lines and wreaked havoc on Northern California commuters.
The Federal Aviation Administration reported arriving flights to SFO were delayed up to 90 minutes and about 175 flights were canceled Friday morning, while Sacramento's regional transit agency reported that a lightning strike had knocked out power to one of its rail lines.
About 170,000 PG&E customers in Northern California had lost electrical power as a result of the storm, with 42,000 still without power by the evening, the company said.
The storm started off the Pacific Coast and was swooping as far south as Monterey before pushing east. Some mountains could receive as much as 10 inches of rain through the weekend, the National Weather Service said. The rain totals were only about half an inch in San Francisco.
"It's horrible," CHP public safety dispatcher Susie Nasca said of road conditions on I-80 near the Donner Pass, close to Truckee in the Sierra. Numerous car accidents and big rig jackknifings were reported, but she said she did not know of any serious injuries.
No deaths were reported on Nevada highways, but at least a dozen people were hurt in crashes when dust storms blinded drivers and several trucks overturned.
Winds gusting to 134 mph over ridge tops early Friday closed several ski resorts around Lake Tahoe, snapped dozens of trees, downed power lines and sparked small brush fires.
Fire-scarred hillsides could get even more rain by the end of the weekend, triggering mudslide warnings for residents. Businesses in Marin, Napa, Solano, and Sonoma counties stacked sandbags to prepare for possible flash flooding. Forecasters also predicted that the peaks of the Sierra Nevada could get as much as 30 inches of snow.
The storm is riding an atmospheric river, also known as the Pineapple Express, which is a band of warm, wet Pacific air.
"It acts like a river moving through the atmosphere, raining copiously on things below," said National Weather Service forecaster Diana Henderson.
The storm won't make a significant dent in the state's historic drought, but it was a big change after six dry weeks in the Bay Area. The storm is expected to get weaker as it moves south, with less than a quarter-inch of rain forecast for Los Angeles.