Last Updated 3:01 p.m. ET
SAN FRANCISCO Northern California is bracing for more stormy weather this weekend after heavy rain and strong winds knocked out power to thousands, delayed flights, tied up traffic and flooded some roadways.
After the second in a series of storms slammed the region Friday, scattered showers are expected Saturday before a third storm strikes Sunday morning, according to the National Weather Service.
Flood warnings have been issued for the Napa and Russian rivers.
Forecasters say the Napa River is expected to rise above flood stage around noon Sunday near the city of Napa and near St. Helena, while the Russian River is expected to flood near Guerneville early Monday morning.
Besides the danger of flooding, forecasters are also warning about the possibility of mudslides and of trees falling in the area because the ground is saturated from the previous storms.
A flash flood watch is also in effect for a wide area of Northern California through Sunday evening, including most of the San Francisco Bay Area and the Santa Cruz Mountains.
The storms could cause rock and mud slides in areas already saturated and affected by wildfires this summer, said NWS forecaster Diana Henderson in Monterey.
"It's not a super storm by any measure, but this is pretty significant," Henderson said. "We should see periods of moderate to heavy rains."
Friday's stormy weather may be behind the death of a Pacific Gas & Electric worker in West Sacramento who was killed after his truck crashed into a traffic signal pole during the stormy weather.
Friday's storm delayed flights at San Francisco International Airport and knocked down a large tree that smashed a car and blocked a busy street for hours in the city's affluent Pacific Heights neighborhood.
The North Bay was seemingly hit the hardest, as parts of Sonoma County received more than 7 inches of rain and areas in Napa County received nearly 6 inches, Henderson said.
With rain expected all weekend long, Tony Negro, a contractor from Penngrove, Calif., in Sonoma County, said he is worried about water flooding his workshop.
"I'm on my way to get some sand bags," he said.
Thousands of people were without power in that area after an outage that also affected the San Francisco-Oakland Bay Bridge. The suspension span of the bridge was briefly in the dark as traffic was backed up longer than usual because of rain and strong wind gusts.
Also, a mudslide shut down a stretch of Highway 84 east of Fremont, the California Highway Patrol reported. There was no estimate on when it would reopen.
In Sacramento, an empty big-rig jackknifed in the southbound lanes and struck the median divider on Interstate 5 south of downtown Friday morning, the CHP said.
"I would definitely say it's weather-related. The reports came in that he hit a water puddle and hydroplaned and couldn't correct," CHP Officer Mike Bradley said. "A lot of high-profile vehicles, especially the lighter ones, are getting windblown and having some problems maintaining their lane."