The National Weather Service has issued a dense fog advisory that is expected to be in effect until 11 a.m. today.

The advisory means widespread visibility of less than one-quarter mile is expected.

The National Weather Service recommends drivers slow down and leave plenty of space between cars.

Roads could be slippery because of the fog, and drivers should use their headlights.

San Francisco, Santa Cruz, San Mateo, Marin, Monterey, Contra Costa, Napa, Sonoma, Santa Clara and Alameda counties are included in the advisory.