Season’s heaviest rainfall expected this week

Ahead of what is forecast to be the region’s largest storm so far this wet season, the National Weather Service on Sunday issued a flash flood watch for much of the North Bay and warned that strong rainfall could trigger debris flow in the region’s numerous recent wildfire burn scars.

The flood watch starts Tuesday afternoon, corresponding with the arrival of an atmospheric river, and will last through Thursday afternoon, impacting a vast swath of western California, from south of Big Sur to Napa, and it includes all of Sonoma County.

Flooding danger is likely to be preceded by fierce winds, according to a National Weather Service wind advisory for many of the same areas Sunday night and Monday morning.

Consistent northwest winds are expected to reach up to 30 mph between Sunday night and 10 a.m. Monday, while gusts will top out at 50 mph, said Brayden Murdock, meteorologist with the National Weather Service in Monterey. That will lead to coastal hazards such as rip currents, ocean swells and sneaker waves just before the arrival of an atmospheric river to the North Bay Tuesday night.

“It’s not exactly a good time to be out and about at the beaches,” Murdock said. “When we start seeing winds that strong, we get worried about already damaged trees falling over, the power lines and high-profile vehicles. And then, that’s where we start to worry about the midweek stuff as well.”

Following some light weekend showers, weather models are holding, Murdock said, with rainfall in the Santa Rosa area projected at between 4 to 6 inches through Wednesday evening, and as much as 8 inches at higher elevations.

“This is going to be our most significant rainfall so far in the water year. Unfortunately, even if get some of higher amounts forecast in that area, it will still only be at halfway point of average,” he said.

In the 2020 burn scars of the Meyers and Walbridge fires, Glass fire, as well as the Woodward fire in the Point Reyes National Seashore, residents should be ready to evacuate in case of power outages, debris flow and possible flooding. Combined with heavy wind gusts, Sonoma County should prepare for heavy precipitation through at least Wednesday, with some light showers lingering into Thursday.

“So it’s going to be a lot of rain, and it’s going to be coming at you fast,” Murdock said.