Bay Area Braces for 5 Days of Rain From Atmospheric River Storm

Updated 12:45 p.m. Monday

After a dry fall, the Bay Area is bracing for heavy rainfall this week that’s set to push Northern California significantly ahead of its seasonal average for this time of year.

The season’s first atmospheric river will arrive Tuesday night, bringing five days of fairly continuous rainfall to the Bay Area, according to National Weather Service meteorologist Nicole Sarment. The North Bay will be hit hardest and first, with Napa and Sonoma expected to get 4–6 inches of rain inland and 7 inches on the coast between Wednesday and Thursday night. Up to 10 inches could fall in areas north of Healdsburg.

San Francisco could also be hit with up to an inch and a half of rainfall during the first wave of the storm, which is made up of two low-pressure systems, according to Sarment.

She said that after the first sweeps through midweek, the second is expected to begin Friday and extend through the weekend, reaching farther south and inland.

Significant rainfall is again likely in the North Bay and San Francisco this weekend. Both regions are forecast to get about the same amount of rain as earlier in the week, if not slightly less. As the storm pushes south, it’s expected to lose steam, with total rainfall predictions under an inch in the South Bay, except for the Santa Cruz Mountains.

The storm could set Northern California ahead of its seasonal rainfall average for mid-November — which had appeared unlikely after a drier-than-usual fall.

“It would definitely put us above normal,” Sarment said.

San Francisco usually sees about 2.4 inches of rain by this point in the year but has only gotten about 0.6 inches since the water year began on Oct. 1. After the storm, the city is predicted to be at about 3.6 inches.

The North Bay could shoot past its seasonal averages, too, which are about 3.5 inches in Sonoma and 1.7 inches in Napa.

“Our winter and our rainy season is definitely early here in Sonoma County,” said Jeff DuVall, the county’s director of emergency management.

Despite the significant precipitation in the forecast, Sarment and DuVall said the flooding risk doesn’t appear to be high. Because of the dry fall, soil isn’t already highly saturated, and the long, consistent pattern of the storm should lessen pressure on drain systems.

“What we will see is the potential for some flood advisories pushed out for small streams, creeks,” DuVall said.

Officials do not expect major rivers like the Russian River to approach the monitor stage, at which preparations for potential flooding would be recommended.

“We are expecting a lot of rain, but something really important to point out is that we’re not, as of this time, expecting any mainstream river flooding,” Sarment said. “There’s between a 0%–5% chance we can’t completely rule out, but that’s not in the forecast at this time.”

San Francisco tends to see higher risk when rain falls at a rate above an inch at a time, making it unlikely this week will see flooding there, barring blocked drains or an unexpected road obstruction.

“I’m not trying to undercut what we’re expecting, but [that’s] the good news,” Sarment told KQED.

Still, people should prepare for rainy, windy conditions as much as they can. Sarment advised people to clean out gutters, identify any trees that might have loose branches or roots on their property, and secure outdoor furniture that could be blown away.

Once the storm starts, it’s important to look out for downed power lines that could be active and avoid driving into flooded areas.

“Honestly, it would just be a good weekend to stay home and just stay out of the way,” she said. “I’m sure there’ll be trees down, power lines down, and all that kind of stuff.”

KQED’s Ezra David Romero contributed to this report.