SAN FRANCISCO (CBS SF) — An ‘Atmospheric River’ storm front, packing intense downpours and gusty winds, was poised Friday off the California coast, ready to make the Bay Area’s evening commute a challenging journey home.

Forecasters said the storm would roll into the North Bay by Friday afternoon with up to 3 inches falling in the hills and coastal mountains by the time the cold front moved through late Saturday.

A flash flood watch for the 77,758-acre burn zone left from October’s massive Kincade Fire was set to begin at 4 p.m. and last until 4 a.m. Saturday.

“Given the dynamics with the potent cold front and ample moisture, rainfall intensity will be of concern across the North Bay, especially in the Kincade Burn area,” the National Weather Service said. “Hourly rainfall rates could exceed one half an inch in an hour leading to debris flows or flash flooding.”

Sonoma County officials have been busy, placing straw waddles around storm drains, along highwauy culverts and ditches, trying to protect the soil from washign away.

“We have patrols from our county Public Works Dept in the area, making sure that they’re watching out for any kind of movements or debris flows or slides,” said David Rabbitt from the Sonoma County Board of Supervisors. “Knock on wood, we did well last week. We hope we do well this week.”

The rain was expected to arrive in San Francisco around the evening rush hours, making travel on local roadways hazardous.

The National Weather Service has posted a wind advisory for the Bay Area, predicting steady winds of 15 to 30 mph with gusts up to 50 mph until Saturday morning.

“Downed trees and downed powers lines may lead to travel hazard or power outages,” the weather service warned. “Use extra caution when driving, especially if operating a high-profile vehicle.”

Forecasters predicted by the time the storm completely passes through early Sunday — 3-4 inches of rain could fall in the North Bay hills, 1.5-3 inches in the Santa Cruz mountains, half an inch in the Silicon Valley and up to an inch elsewhere.

In the Sierra, the weather service has issued a winter storm warning that will run until noon on Sunday.

The storm was predicted to bring as much as another 3 feet of snow possible in the upper elevations by early Sunday. Snow levels Friday will start around 7,000 feet and fall into the 6,500 foot range in the evening.

That is on top of the more than 3 feet of snow fell at Tahoe-area ski resorts during a seven-day stretch a week ago.

“Travel could be very difficult to impossible, especially over the Sierra passes,” the weather service warned. “The hazardous conditions are likely across passes through at least Sunday morning. Gusty winds and heavy, wet snow could bring down tree branches.”

Caltrans warned Bay Area travelers headed to the Sierra to expect chain controls to be in effect on the mountain passes on Highway 50 and I-80.

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