The National Weather Service has issued a flash flood warning for Sonoma County Saturday afternoon that includes the cities of Petaluma and Rohnert Park.
The warning was issued around 1:40 p.m. and will be in effect through around 7:45 p.m., according to the National Weather Service.
The warning applies to the area to the west of Laguna De Santa Rosa, western Rohnert Park, the lower portions of Mark West and Windsor creeks and eastern Petaluma.
A flash flood warning means flooding is already happening or is imminent, according to forecasters.
The warning comes as Sonoma County and the Bay Area are pelted with heavy rain, causing flooding in creeks, streams, underpasses and other low-lying spots.
In the North Bay, driving has been treacherous all day long, and some roads were even impassable. And with the rain still falling, there is no sign the water is receding.
"Just take it real slow, especially when you get deep water like this," one driver said. "It's a lot safer that way."
Earlier Saturday, a mudslide caused part of Fort Ross Road near Cazadero to slide down a hill and toward a house that had already been evacuated. That road has been closed indefinitely.
And in Rohnert Park, part of Millbrae Avenue near Whistler Avenue was washed out by a nearby creek. Some drivers were turning around, but others went right through the water.
Also, Rohnert Park Expressway between Stony Point Road and Redwood Drive is closed because of flooding.
National Weather Service officials are advising people in the area not to try to cross quickly flowing water or water of unknown depth and to be especially cautious at night when it's harder to spot flooded areas.
If flash flooding occurs, people are advised to move quickly to higher ground and leave any low-lying areas subject to flooding.
UPDATE: The flash flood warning has now been lifted.