The National Weather Service on Thursday issued a variety of warnings for heavy rain, snow, high winds and floods from the San Francisco Bay area to the Oregon border.
Officials say intense rainfall is expected overnight through Friday morning before another storm hits Sunday.
The service says small rivers and streams are at increased risk for flooding, especially in the upper Sacramento River region.
Officials say the storm could cause flooding on roads and trigger rock and mud slides. Gusty winds could knock down trees and electricity lines, leading to power outages.
On the coast there are gale warnings and small-craft and high-surf advisories.
North Bay prepares for flooding as storm moves in
After a brief break, rain is returning to the North Bay. Residents and business owners are preparing for the possibility of flooding, especially in areas that have shown a propensity for problems in the past.
It's a race against the clock and the weather at RS Technical Services in Petaluma, a business that has flooded twice in eight years.
"It all starts to pull in like a pool and it goes under the doors and mud comes through and the floors are all covered, sometimes a couple inches, sometimes a couple feet," Kathleeen Colsen said.
Two more wet systems are poised to move in over the next three days, so they're not taking any chances. With a forklift, sandbags and plastic sheeting, they're hoping this time, they can keep all their high-tech pipe inspection equipment high and dry.
Close to downtown, Bay Bridge Garage has sandbags at the ready too, hoping to avoid the kind of flooding they saw here in 1998, when water made it inside their building.
The issue there is the Petaluma River, which can overflow with heavy rains at high tide.
"Once the water comes up over the ledge here and it starts to seep into the office and gets up to the doors, then we're probably going to have a problem," Kyle Hermsmeyer said.
The Associated Press contributed to this report.