Bay Area Braces for Heavy Rain, Fierce Winds During Thursday Morning Commute

Wind. Downpours. Thunderstorms. Potential power outages.

National Weather Service forecasters expect this week’s atmospheric river to bring heavy rain and fierce winds across the Bay Area late Wednesday evening into Thursday.

Meteorologists expect the North Bay to receive between 1.25 and 5 inches of rain, with more precipitation at higher elevations, such as Mount Tamalpais. The East Bay could receive under an inch to more than two inches of rain. Anywhere from an inch to 3.5 inches of rain could fall along the San Francisco peninsula, the South Bay and Santa Cruz.

Roger Gass, a meteorologist with the weather service’s Bay Area office, said he doesn’t expect the atmospheric river to stall, which typically would mean higher rainfall totals.

He said the heaviest rainfall could happen around commute time on Thursday morning.

Forecasters expect the system moving toward the region from the Pacific Ocean to “pack a punch” when it comes to winds along the coast. A high wind warning is in effect from 10 p.m. Wednesday through 10 a.m. Thursday morning for the coastal North Bay, the Marin hills and down the San Francisco Peninsula, with gusts potentially exceeding 60 mph.

As for the rest of the region, the service issued a wind advisory for the same time period, with winds up to 25 mph and gusts up to 50 mph.

“Just be ready for isolated to widespread power outages as weaker trees and limbs fall in these wind speeds,” Gass said. “I would encourage folks to delay travel in the morning, if they don’t have to be anywhere, as it’ll be during the brunt of the rush hour traffic.”

An atmospheric river is a massive corridor or “river” of concentrated water vapor in the atmosphere that can behave erratically, soaking a region when it stalls. Weather experts measure the intensity of atmospheric rivers on a scale from 0 to 5.

This week’s storm could reach a 3 across the entire Bay Area, according to atmospheric river-scale modeling by the Center for Western Weather and Water Extremes at UC San Diego’s Scripps Institution of Oceanography.

Daniel Swain, a climate scientist with UC Agriculture and Natural Resources, said in his weekly YouTube “office hours” that while the “storm looks pretty robust,” he doesn’t expect it “to be a huge precipitation event for the Bay Area.”

Swain said that frequent atmospheric rivers are normal for California, which relies on them to replenish its water supply.

But he said their intensity doesn’t always translate into big rainfall totals or flooding.

“Sometimes, people conflate [that] atmospheric rivers equal a big bad storm,” Swain said. “That’s not always going to be true. Sometimes they’re quite gentle, gradual, or beneficial. Sometimes, though, they can be a big problem.”

Forecasters expect another weak system to bring light rain across the region this weekend and early next week.