Here’s when rain, floods will hit this afternoon

At 4:30 p.m., the cold front was 30 miles offshore but was moving east toward the Bay Area. Moderate rain was falling ahead of the cold front and caused a landslide on Highway 9, three miles east of Saratoga. A downed tree was being held up by power lines over Hwy. 9 in Boulder Creek. Both directions of Hwy. 9 were closed, but California Highway Patrol said the road was expected to reopen by 10:30 p.m.

The National Weather Service extended a flooding advisory until 10 p.m. Friday across portions of the Bay Area because of moderate rain and roadway flooding.

Marin County received especially an especially heavy dowsing Friday evening, with National Weather Service forecasters tweeting that Mt. Talampais was expected to have “impressive rain totals” when the storm was “all said and done.”

Flooding was also reported in Alameda, San Mateo, San Francisco, Santa Cruz and Sonoma counties.

The light rain showers turned into heavy downpours later in the day when a line of heavy precipitation known as a narrow cold frontal rainband moves through the Bay Area.

The front itself will be quick-hitting, but the storm won’t be finished with the Bay Area quite yet. The atmosphere is expected to become unstable as colder air spills toward the region, creating a favorable environment for thunderstorms Friday night into midday Saturday. Occasional lightning, brief downpours and small hail are the main hazards expected with these thunderstorms.

Showers and thunderstorms should become more isolated Saturday afternoon before subsiding overnight.

Rainfall totals through Saturday are expected to range from three-quarters of an inch to an inch in the Santa Clara Valley and Tri-Valley, 1 to 1.5 inches in San Francisco and Oakland, to 2 or more inches around Mount Tamalpais and the Santa Cruz Mountains.

The weather pattern will be quieter for New Year’s Eve and New Year’s Day, with only a slight chance of rain showers.

Chronicle Staff Writers Clare Fonstein and Maggie Angst contributed to this report.