SAN FRANCISCO -- A potent Pacific storm, borne by an atmospheric river, rolled into Northern California Saturday, kicking up gusty winds that toppled trees in Monte Rio and dumping heavy rain that triggered flash flood watches throughout the Bay Area.
A flood advisory remained in effect from Sacramento to the coast.
Flash flood concerns for the Colorado Fire and Dolan Fire burn scars in Monterey County prompted officials Saturday afternoon to close Highway 1 from Ragged Point in the south to Palo Colorado Road in the north until at least dawn Sunday.
As the storm marched across the region, flood watches were issued for Marin, San Mateo, Alameda and Santa Clara counties.
Meanwhile, gusty winds up to 50 mph toppled trees and limbs into several homes in rural Sonoma County.
On Alder Dr. in Monte Rio, a tree slammed into a two-story home. Over on River Blvd., a large redwood branch fell, damaging three vehicles and an Airbnb rental.
"It was like an earthquake," said Cynthnia Cook, one of the Airbnb renters who was in town from Pacifica to celebrate a friend's birthday. "A redwood branch came down and hit all three of our cars that aren't operational right now."
Later a tree fell into a house on Old Monte Rio Rd. in Guerneville. The tree brought down power lines, along with the top half of a utility pole, blocking Highway 116 for about 30 minutes.
In the Santa Cruz Mountains, where nearly 3 inches had fallen by 2:15 p.m. at Ben Lomond, the CHP was reporting two large "basketball-sized" boulders blocking the right lane on southbound Highway 17 before the summit.
In San Francisco's Golden Gate Park, a massive redwood fell in Hellman Hollow, forcing organizers to alter the race course at the National Club Cross County Championships.
"The tree was a Monterey Cyprus, approximately 30 feet tall," a spokesperson for San Francisco Recreation & Parks told KPIX. "It went down around 10:30 a.m. No injuries and we relocated the race to the upper Polo Fields track."
The storm arrived before dawn and immediately grew in intensity.
"Rain looks to become widespread around the S.F. Bay Area by around sunrise, with heaviest rain and strongest winds just ahead of and with the cold frontal passage," weather service forecasters said. "Timing for that looks to be around mid-morning in the Santa Rosa area, late morning for San Francisco and mid-afternoon around Monterey Bay."
Of particular concern is the San Lucia range in Monterey County. It will be ground zero for the storm's ire. A flash flood watch will remain in effect for the entire day.
"Forecast grids for just the 12-hour period now call for close to 7 inches of rain wettest portions of the Santa Lucia range," the weather service said. "For the burn scars of the Dolan, River and Colorado Fires especially, raises significant concern over the possibility of localized flood or debris flows."
Researchers at Scripps Center for Western Weather and Water Extremes predicted the incoming storm front will be a Category 1 or 2 on their atmospheric river scale depending where you are on the coastline.
Most of California will be at the Stage 1 level and Oregon will be pounded by a Stage 2.
"High moisture associated with an Atmospheric River will promote heavy mountain snow as well as heavy rain with showers and thunderstorms for lower elevations along the coast," the National Weather Service predicted. "The highest snow totals are currently expected for the Sierra Nevada in California where several feet of snow is forecast."
The storm was expected to dump more than two inches of rain in the Bay Area and bury the Sierra under several feet of snow. As it stands now, amounts close that have been seen in the Santa Cruz Mountains and Marin County, with the area around the Marin County Civic Center in San Rafael seeing about 1.5 inches of rainfall by 11 a.m. Saturday.
"An additional concern will be more widespread minor urban and small stream flooding as soils are increasing becoming saturated," the weather service said of the storm's impact in the Bay Area.
A high wind advisory has also been issued for the region with wind gusts up to 50 mph predicted.
In the Sierra Nevada mountains, a winter storm warning extends all the way to 4 a.m. Monday. More than four feet of new snow was forecast for Donner Summit and Kirkwood with just about three feet expected at Truckee.
"Snowfall rates of 1 to 3 inches per hour for several hours through Saturday and into Sunday, leading to significant snowfall totals of 2 to 5 feet," the weather service said.
But the snow will not be light and fluffy.
"This portion of the storm will be heavy, wet Sierra cement type snow due to the subtropical moisture with snow ratios 8 to 1," the weather service said.
The U.S. Forest Service has activated a backcountry avalanche watch in the central Sierra including Tahoe and warned of higher avalanche danger Saturday into Sunday.
"A winter storm with gale force winds, high intensity snowfall and feet of new snow accumulation may result in widespread avalanche activity in the mountains," the Avalanche Center said.
Authorities also urge motorists to stay off mountain roads in the Sierra through the weekend.
"You could be stuck in your vehicle for many hours," the weather service in Reno warned.
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