The flood watch includes Del Norte, Humboldt, Mendocino, Trinity and Shasta counties, among others. The region faces the potential for mudslides and road closures.
A flood warning has already been issued for the Eel River at Fernbridge, where flooding could affect local highways and farmland.
The Russian River near Hopland is also expected to flood on Tuesday afternoon.
Doug Boushey, a forecaster with the National Weather Service in Eureka, said road closures are likely.
"The flood watch that we have out right now is for what we call aerial flooding, smaller rivers, streams, creeks, low-lying areas with poor drainage that tend to flood," he said.
Boushey said there’s also the potential for mudslides in the region. He encourages residents to be careful while driving and to not try to drive across a road that has flooded.
This level of flooding is unusual for March, Boushey said. The weather is being caused by one of a series of atmospheric rivers, which have recently been bringing moisture to California from the tropics.
"It's kind of a double-edged sword. On the one end, you know, this is great for the drought mitigation, and we've certainly been seeing the drought map getting whittled away slowly but surely. Then with these atmospheric river storms comes the threat for flooding," Boushey said.
He said they're not expecting any flash flooding.
Sergeant Chris Van Eyck with the Shasta County Sheriff's Office said they’re expecting flooding in smaller rivers and creeks, but not in bigger bodies of water like the Sacramento River.
"We're looking more for localized flooding," he said. "Localized flooding as far as streams and contributors to the river, depending on debris and other factors."
He said there is sufficient storage space behind the Shasta and Keswick dams, so water will not need to be released from the reservoirs.
Van Eyck added that his office will watch for potential power outages and warned that higher elevations could see snow as well.
The Sheriff’s Office is providing sandbags to residents to help with flooding concerns.
