The new onslaught of rain comes as Southern California dries out following downpours that left five people dead.
A flood warning is in effect for Northern California's interior counties through Thursday. Storms started overnight Saturday, with two to four inches of rain expected by Wednesday, CNN meteorologist Allison Chinchar said. Some areas may get up to 10 inches and the driving rain could drastically reduce visibility, Chinchar warned.
The National Weather Service said the storms carried a threat of flooding, mudslides and would make travel potentially dangerous.
The brunt of the latest storm system was predicted to hit the West Coast on Sunday afternoon. Forecasters expect heavy rain throughout Monday for much of Northern California. Another storm is expected to hit the area Tuesday into Wednesday.
Northern California is already soaked from heavy rains that have pummeled the state since early January. Additional stress on levees, dams, rivers, creeks and streams is expected.
The National Weather Service in Sacramento on Sunday was advising all residents in Northern California's interior to prepare for flooding and possible evacuations.
Officials are keeping an eye on the Oroville Dam after mandatory evacuations last week over concerns that an emergency spillway could fail and threaten nearby communities.
Officials cautiously optimistic
Rain began in the area early Sunday and is expected to continue until Wednesday, according to the National Weather Service. A flood warning is in effect until Thursday.
Residents have since returned home and officials expressed cautious optimism despite the rainy forecast.
As of Sunday afternoon Lake Oroville's water level was at 852 feet, 49 feet below spill level, California Department of Water Resources spokesperson Chris Orrock told CNN.
"There is a chance that we may see a slight increase in the water level, but we now have plenty of room to absorb water that may be coming into the lake with the coming storm," Orrock said.
Crews have reduced the outflow by 30%, allowing teams to clean up debris below the dam, the tallest in the United States.
The amount of water flowing into Lake Oroville -- 37,000 cubic feet per second -- is much less than the 60,000 cubic feet per second allowed to flow out through the dam's primary spillway,
Winter storm warnings
Power went out and cars were submerged in Southern California after the region experienced one of its most drenching storms in recent years. At least five people died.
In Victorville, San Bernardino County, one person was found dead Friday in a flooded vehicle, firefighters said. A second storm victim, a 55-year-old man, was electrocuted when a power line fell Friday in Sherman Oaks, west of downtown Los Angeles, the fire department said.
On Saturday, the Thousand Oaks Police Department said a body was recovered from a river gorge. Police didn't give any details.
Two people died Saturday evening after an accident in San Diego on Interstate 15, California Highway Patrol Sgt. Nicole Pacheco told CNN.
Rainfall totals from the National Weather Service
showed parts of Santa Barbara County had seen more than 7 inches of rain in two days. Parts of Ventura County saw more than 6 inches.
The storm has also blanketed higher elevations with snow.
With more rain expected, some cities in the Pacific Northwest have already seen some of their wettest Februarys ever.
- Seattle is already at its fifth-wettest February.
- Portland, Oregon and Spokane, Washington are at their sixth.
- Salem, Oregon is at its seventh.