The latest storm system -- the third to hit the area in less than a week -- moved across the region late Saturday and early Sunday dropping as much as an inch of rain per hour in some areas, toppling trees and knocking out electrical service to tens of thousands of people, officials said.
With rivers across Northern California swelling from the deluge, the National Weather Service warned that several rivers were in danger of topping their banks Sunday afternoon or early Monday.
Flood warnings were in effect for the Napa and Russian rivers, two rivers north of San Francisco with a history of flooding, as well as the Truckee River, near Lake Tahoe.
"We've been in preparation mode since Thursday," said Barry Martin, a spokesman for the city of Napa.
In bracing for the storm, city officials had handed out more than 8,000 sandbags and about 150 tons of sand, Martin said.
The Napa River was expected to surpass flood stage Sunday afternoon, though most of the flooding was expected to be in agricultural areas outside of the city of Napa, officials said.
In Sonoma County, the Russian River was expected to top its banks Monday morning, forecasters said.
Elsewhere, officials prepared for flooding near Truckee, Calif. a small town of about 16,000, as the Truckee River neared the top of its banks.
Truckee officials had set up an evacuation center in a school district building but by early Sunday no area residents had showed up at the center, said Mike Fitch, a spokesman for the Placer County Office of Emergency Services.
"They're pretty resilient," Fitch said in describing the area's residents. "And we do have a lot of vacation homes up here," he said.
Despite the severity of the storm, weather officials were heartened by the speed in which the system moved through the area, meaning rainfall amounts could be less than predicted. And with colder temperatures than expected in the mountains, more snow and less rain fell.
"I'm not sure by how much it could lower the flood threat yet," said Gary Barbatgo, a NWS hydrologist said early Sunday. "Maybe dramatically but we'll have to see," he said.
In far Northern California, flood warnings remained in effect Sunday for the Eel, Navarro and Mad rivers.
Meanwhile, around 94,000 people from Santa Cruz to Eureka, including about 21,000 people in the San Francisco Bay area, were without electricity Sunday as the powerful winds from the storm knocked down trees and sent broken tree limbs and branches across power lines, said Pacific Gas & Electric spokesman Joe Molica.
"It really did broadside California," Molica said of the storm.
About 2,000 PG&E crews were working Sunday to try to restore power, Molica said.