The National Weather Service issued a flash flood watch for the North Bay, including Napa County, from 4 p.m. Wednesday through 3 a.m. Thursday.
As much as 1 to 2 inches of rain could fall in North Bay valleys and 2 to 3 inches in mountain areas impacted by the recent Atlas, Tubbs and Nuns fires, the Weather Service said.
Because of the wildfires, the Weather Service warns of possible debris flows and mudslides on land with burn scars.
More than 70,000 acres within Napa County have burned. Vegetation that normally covers the hillsides is gone, creating the potential for higher levels of erosion and debris movement, county officials said.
Officials noted that the ground is far from saturated at this point in the rain season.
A flash flood watch alerts the public to the possibility of a dangerous condition. It could be followed by a flash flood alert if heavy rains occur as forecast.
Conditions should improve Thursday, with showers predicted. Friday and Saturday will be sunny, with a chance of rain on Sunday, the Weather Service said.