The San Mateo and Bay bridges both have been issued fog advisories early this morning, according to the California Highway Patrol.
As of 2 a.m. visibility on the Bay Bridge was down to 300 feet, the CHP said.
At 5:03 a.m. a dense fog advisory was issued in east Contra Costa County, the CHP said.
Overall visibility in the Bay Area, especially along the Bay, is less than a half-mile in many areas, according to the National Weather Service.
Weather officials issued an alert at 10 p.m. Monday night. The alert is effective until 9 a.m.
On other Bay Area bridges and roads, foggy conditions are affecting visibility, according to the CHP.
Drivers on the Golden Gate and Dumbarton bridges, in San Francisco, Marin and Alameda counties, respectively, have been advised about heavy fog. An advisory went into effect just after midnight this morning for both bridges.
Fog advisories are also in place as of midnight in Marin and San Mateo counties.
Affected areas include state Highway 37 from U.S. Highway 101 to the Solano County line and state Highway 1 from Interstate Highway 280 to Pacifica, according to the CHP.
