Incoming downpour now forecast to hit midday Sunday

A major storm caused a flash flood warning, high tide advisory and wind advisory to be issued for Sunday, with the most severe weather expected late morning or early afternoon.

“Most things are on track, but over the last 12 to 16 hours the timing has slowed down a bit,” National Weather Service meteorologist Eleanor Dhuyvetter said Saturday night.

“It looks like Sonoma County is getting pretty good rain right now, but the bulk of the rain will hit midday Sunday,” she said. “The valleys will get 3 to 6 inches, probably, and 4 to 6 inches will fall in the lower elevations. In the higher terrain, the highest peaks of the Mayacamas Mountains on the eastern border of Lake County could get upwards of 10 inches.”

The heavy precipitation is caused by an atmospheric river, or a large stream of moisture coming from the Pacific Ocean. As a cold front interacts with warm air, it creates precipitation that acts as a fire hose pointed at the Bay Area, said Brayden Murdock, meteorologist for the National Weather Service.

The last atmospheric river to hit Sonoma County was in late January, when the region saw heavy rain, gusting wind up to 60 mph, toppled trees, power outages and a foot or more of snow on the mountaintops. That storm brought only a couple of inches of rain, despite forecasts of 5 or 6 inches.

In the 24 hours ending at 9 p.m. Saturday, the county had received about ¼- to ½-inch of rain in the lower-lying areas and upward of an inch in high elevations, especially toward the coast, Dhuyvetter said.

The heaviest rain will start in the northernmost areas of Sonoma County late morning to early afternoon. But heavy winds will begin around 5 or 6 a.m., she said.

With the heavy rain comes serious concerns for flash flooding, particularly for areas that were burned last year in the west county during the LNU Lightning Complex fire and east of Santa Rosa in the Glass fire.

The weather service has issued a flash flood watch from 5 a.m. to 11 p.m. Sunday. Anywhere with concrete and low drainage also is a concern for flooding because water won’t be able to escape and absorb into the soil, Murdock said.

The Russian River estuary remains closed due to high potential for water levels to exceed 9 feet, according to Sonoma Water in a media release.

The weather service also issued a wind advisory for the North Bay from 2 a.m. to 5 p.m. Sunday.

Winds are expected to begin building early Sunday morning, particularly in the higher elevations, which could see gusts of up to 50 mph. In the valley areas, the gusts may reach as high as 40 mph, Murdock said. They will last until about 5 p.m., and then will be slow to diminished, ending with calm winds, Dhuyvetter said.

The atmospheric river will bring a change in ocean flow resulting in dangerous, choppy conditions, sneaker waves and rip currents Sunday morning through Tuesday morning, meteorologists warned.

The National Weather Service issued a high surf warning in the North Bay area, with large breaking waves 20 to 30 feet high at west- and northwest-facing beaches.

Heavy wind and rainfall could result in power outages as well. With the drenched soil, trees could also topple, Dhuyvetter said.

Pacific Gas & Electric Co. customers should prepare for possible outages around the corner, cautioned Deanna Contreras, spokesperson for the company, in a tweet Saturday morning.

Residents, especially those in burn scar areas, can prepare for flash flooding by stocking up on sandbags, clearing debris from gutters and storm drains, and avoiding driving, Murdock said.

The city of Santa Rosa is providing free sand and bags to residents at the Municipal Services Center North at 55 Stony Point Road.

In case of power outages, Murdock advised people to charge their phones and backup batteries, know where to get information from local emergency management and check emergency kit supplies.

“We want folks to stay weather aware and be as prepared as possible,” he said.

You can reach Staff Writer Alana Minkler at 707-526-8511 or alana.minkler@pressdemocrat.com. On Twitter @alana_minkler.