A dense fog advisory was issued Tuesday morning across the Bay Area, according to the National Weather Service. The advisory is in effect until 9 a.m., the weather service said. Visibility was expected to be a quarter-mile or less in some places, resulting in hazardous driving conditions, especially during the morning commute, the weather service said. The dense fog advisory was in effect for the North Bay, San Francisco, the San Francisco Bayshoreline, the Santa Cruz Mountains, the Santa Clara Valley and East Bay interior valleys. The weather service advises drivers to slow down, use their headlights and leave plenty of space between their vehicle and vehicles in front of them.