Dense fog produced beautiful vistas but made for a difficult Thursday morning commute, prompting fog advisories on several bridges around the Bay Area, including the San Francisco-Oakland Bay Bridge, the CHP said.

Another round of patchy, dense fog is due today before clear mornings prevail again, with daytime weather remaining mostly sunny and clear through the weekend, the National Weather Service said.

Overnight lows will remain on the chilly side after dropping to 31 degrees at the Charles M. Schulz-Sonoma County Airport early Thursday.

The mercury is expected to rise just a few degrees, into the mid- to upper 30s for the next five or six days, meteorologist Diana Henderson said.

Daytime temperatures should be in the 58- to 63-degree range for the next week or so, she said.

Cold, still air conditions have prompted the Bay Area Air Quality Management District to declare a third consecutive Winter Spare the Air day for Friday.

Burning of wood logs and other wood products is prohibited except in cases where wood fire is the only source of space heat.

-- Mary Callahan