Atmospheric river storm slams NorCal; Bay Area sees widespread flooding

A third day of an atmospheric river storm has inundated Northern California and the Bay Area, with the storm spreading from the North Bay south across the region, flooding creeks, roads, and low-lying areas.
The relentless downpour prompted the National Weather Service to issue flash flood warnings for several Bay Area counties Friday afternoon and the city of San Francisco. The flash flood warnings covered northwestern San Mateo County, northwestern and central Alameda County, and west central Contra Costa County.
Earlier Friday, the Weather Service issued a flood warning in Sonoma County for the Russian River at Johnson’s Beach in Guerneville from 2 p.m. Friday until further notice. The warning also applies to the communities of Forestville, Monte Rio, and other areas near the river west of Guerneville. The river was expected to rise above flood stage late Friday evening and rise to 32.5 feet just after midnight. 
The Weather Service reported Friday that the 3-day rain total in Santa Rosa was 12.47 inches, breaking the previous record of 9.96 inches set in October 2021. It is the most amount of rain that has fallen in a 72-hour stretch since records began in 1902. 
North of the Bay Area, a flood warning was issued for several rivers in counties closer to the Oregon border, including the Russian River and Navarro River in Mendocino County, and the Mad River, Eel River, Van Duzen River in Humboldt County. Major flooding is expected along the Eel River affecting the communities of Fernbridge, Scotia, Bridgeville, Fort Seward, and Miranda.
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The city of Sacramento was forecast to see a month’s worth of rain in just 24 hours on Friday. The city averages about 1.78 inches of rain in November; from Friday into Saturday, the city is projected to see just over two inches of rain, adding to the already 1.29 inches of rain the city received this week.
The Sierra Nevada was projected to see whiteout and blizzard conditions as the atmospheric river turns into snow as it reaches higher elevations. While Thursday’s storm brought mostly rain to the mountains, the snow levels will continue to drop through Friday and into the weekend.
The Weather Service said the prolonged rainfall in the North Bay will increase the risk of flooding, landslides, and downed trees and powerlines. Aside from the flood warning, a flood advisory was issued for all of Sonoma, Marin, and Napa counties until 3:15 a.m. Saturday because of expected minor flooding in low-lying and poor drainage areas.
In Sonoma County, the Silverado Trail was closed Friday afternoon from Yountville Cross Road south to Oak Knoll Avenue because of mudslides blocking the roadway, Caltrans said. Earlier Friday morning, a mudslide along Madrone Avenue in Healdsburg blocked the roadway and damaged some properties. Crews were waiting for the rain to subside in order to shore up the hillside.
The ongoing storm prompted dozens of school closures in Sonoma County, closures that have increased since Wednesday. The county’s Office of Education posted an updated list of closures on its website.
In Marin County, the San Rafael Fire Department reported multiple areas of street flooding just after 2 p.m. Friday. San Rafael police also reported multiple calls of trees coming down, including a large tree that fell onto the roadway on Las Gallinas Avenue near Las Colindas Road.
In addition to the rain Friday, southerly winds will increase ahead of the cold front moving south across the Bay Area. The Weather Service also issued a wind advisory until 10 p.m. Friday for coastal and higher elevation regions of the North Bay, the city of San Francisco, the East Bay and Santa Clara Hills, the Santa Cruz Mountains and Peninsula coast, the Gabilan Range, the Santa Lucia Range, southern Monterey Bay, and coastal Big Sur.
Sustained wind speeds will range from winds 15 to 30 mph with gusts up to 50 mph expected in higher elevations. Wind gusts greater than 65 mph are possible above 2,500 feet.