Atmospheric River Headed For Sonoma County, North Bay

SONOMA COUNTY, CA — An atmospheric river with origins near Hawaii will take aim at Sonoma County, the North Bay and the greater San Francisco Bay Area beginning Tuesday night, according to the National Weather Service. A flash flood watch goes into effect at 10 p.m., with rainfall rates of at least half an inch per hour possible during the heaviest showers, officials with NWS SF Bay Area said.

"Recent rainfall has saturated soils across the area, and the additional heavy rainfall will create the potential for widespread shallow landslides, rockslides, and debris flows," forecasters said. "Periods of heavy rainfall will likely inundate storm drains with rapid rises on small creeks and streams."

FLASH FLOOD WATCH: 10 P.M. Tuesday, Feb. 12 through Thursday morning, Feb. 14

The NWS flash flood watch continues through Thursday morning for: coastal North Bay including Point Reyes National Seashore, the interior valleys and mountains of the North Bay; and in Sonoma and Napa counties, the cities of Santa Rosa, South Santa Rosa, Napa, San Rafael, Petaluma, Novato, Rohnert Park and Angwin.

"A flash flood watch means that conditions may develop that lead to flash flooding," weather officials said. "Flash flooding is a very dangerous situation. You should monitor later forecasts and be prepared to take action should Flash Flood Warnings be issued."

The flash flood watch continues for the entire San Francisco Bay Area and Central Coast except for the hills of San Benito County and the East Bay Valleys, according to the NWS.

Forecasters said the Wednesday morning commute will be adversely impacted with flooding roadways and ponding of water expected.

"Periods of heavy rain are also possible during the Wednesday afternoon and Thursday morning commutes," weather officials said.

RIVER FLOODING OUTLOOK

According to the NWS:

"Mainstem rivers, from the Russian and Napa Rivers in the North Bay to the Carmel and Big Sur Rivers farther south, are forecast to see significant and rapid rises beginning on Wednesday and peak on Thursday and Friday. As of Tuesday morning, projections for our mainstem river forecast points indicate only the Russian River at Guerneville exceeding flood stage of 32 feet Friday morning. A few other forecast points are forecast to exceed monitor stage.

"These include the Napa River at Saint Helena and the Napa River at Napa, also the Pajaro River at Chittenden. Although these are the only sites currently forecast to meet or exceed these levels, changes in rainfall amounts received could result in these or other sites approaching or even exceeding monitor or flood stage. Smaller rivers and streams could flood, especially if heavy rain rates persist across a particular watershed. Flooding is most likely in the more typically flood prone low- lying areas.

"In addition, heavy rain rates over the North Bay burn scars could potentially trigger flash flooding or mudslide/debris flows. Away from the burn scars, shallow landsliding could also be a concern if precipitation rates and intensities are sufficient. Latest data from USGS research instrumentation in the San Francisco Bay Area indicates that shallow soils on steep hill slopes are at or near saturation."

The City of Healdsburg said it was not expecting the rain to flood Foss Creek or the Russian River. However, the Healdsburg Fire Department will have extra staff on duty, and city staff will be monitoring the weather and providing updates if weather conditions change, city officials said Tuesday in a social media post.

WIND ADVISORY: 10 P.M. Tuesday, Feb. 12 through 10 A.M. Thursday, Feb. 14

"A wind advisory means that winds of 35 mph are expected," NWS officials said. "Winds this strong can make driving difficult...especially for high profile vehicles. Use extra caution."

ADVISORY AREA: North Bay interior valleys, including the North Bay cities of Santa Rosa, South Santa Rosa, Napa, San Rafael, Petaluma, Novato and Rohnert Park.

"Strong winds may blow down limbs, trees, and power lines," NWS officials said. "Scattered power outages are expected."

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