A so-called atmospheric river of rain and powerful wind has triggered massive delays at San Francisco International Airport, knocked down power lines and generally wreaked havoc on Northern California commuters.
The Federal Aviation Administration reported arriving flights to SFO were delayed up to 3 1/2 hours, while Sacramento's regional transit agency reported that a lightning strike had knocked out power to one of its rail lines.
More than 4,000 locations around Sacramento were also without power Friday morning. 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 reported.
Fire-scarred hillsides could get even more rain by the end of the weekend, triggering mudslide warnings for residents. Forecasters also predicted that the peaks of the Sierra Nevada could get as much as 30 inches of snow.
The outlook for the Bay Area was less dire. The National Weather Service warned of some localized flooding and strong winds and cautioned drivers that it's "looking like the afternoon commute will get nasty in a hurry with moderate to heavy rain" sweeping as far south as Monterey Bay.
The storm is riding an atmospheric river, also known as the Pineapple Express, which is a band of warm, wet Pacific air that's currently swirling over the northern part of the state.
"It acts like a river moving through the atmosphere, raining copiously on things below," said National Weather Service forecaster Diana Henderson. "It's going to cover everybody."
The storm is expected to move across the state into Nevada by the end of Monday.