Incoming Storm to Bring Widespread Rain to the Bay Area

Update 5:38 p.m. Monday: A storm swirling off the Bay Area’s coast will bring rain to the region this week, albeit much less than meteorologists at the National Weather Service originally forecasted.

The storm stayed further offshore than last week’s forecast anticipated. Meteorologists say that shift will mean less rainfall for the Bay Area and the Central Coast.

“While the overall week can be categorized as wet, there will likely be breaks in the precip throughout,” said NWS’s Bay Area office in its latest forecast discussion, noting that they expect the wettest period for the Bay Area to be Wednesday afternoon into the evening.

The Bay Area’s coastal mountains could see up to 2 inches of rain through Saturday, the North Bay and coastal areas 1 to 1.5 inches and inland valleys up to an inch, according to the latest forecast.

While the NWS is confident in a soaking rain this week, meteorologists note that there is still a lot of uncertainty about this slow-moving storm — meaning the forecast could significantly change in the coming days.

They said the spinning low-pressure system off the coast “adds a level of uncertainty to the forecast,” which they described as “not a slam dunk forecast by any means.”

Original November 8 story below:

The National Weather Service is forecasting the Bay Area’s first major atmospheric river of the season next week.

Between Tuesday and Thursday, a storm could drop as much as 2 inches of rain from Marin to Santa Cruz.

“Some of the higher peaks in the Santa Cruz Mountains and the Sonoma Coast could get even more,” NWS meteorologist Dalton Behringer said. “It looks like it’s going to hit everyone, even as far down south as Big Sur and Central Coast.”

This weather is forecast to hit during the 2023 Asia-Pacific Economic Cooperation (APEC) conference in San Francisco — an event that was already predicted to disrupt traffic and public transit as world leaders gather in the city for the high-security event.

The storm follows a deep, low-pressure system coming from the Gulf of Alaska. It is supposed to drop down the West Coast, and it’s part of an active, progressive pattern that could last into the middle of the month.

The atmospheric river is also expected to drop ample snow in the Sierra Nevada. Still, snowfall totals this early are hard to forecast, Behringer said.

“As of now, it looks to be the first big snowpack producer for them as well,” he said.

By the end of the century, climate change may make these deluges from the sky up to 37% wetter, according to a June 2022 study by Bay Area climate scientists.

The storm is on par with a traditional winter storm event, and Behringer said while there is an active pattern in the atmosphere, he is unsure if additional storms will follow suit.

“We can tell that things are going to come through, but it’s almost impossible to nail down details of exactly how strong they will be or where they’ll set up,” Behringer said. “But this will be the first major event of the season.”

Behringer said he does not expect widespread flooding from this storm and said it is too early to provide other details like wind speeds.

“That could change if this system decides to stall in one area versus another,” he said. “The silver lining is that we’re not nearly as saturated as we were when we had these rapid succession events last year.”

He said the storm would likely move pretty quickly over the Bay Area, but if last winter’s storms taught Behringer anything, it’s that movements within a weather pattern can change fast. He advises Californians to pay close attention to weather reports as the storm progresses and to prepare their homes for what could be the first of many Bay Area-wide storms this fall and winter. Read more about how to prepare your home for a storm.

“Keeping up with the forecast right now is the best preparation you can make,” Behringer said. “We’re still putting the finishing touches on the changes to the forecast.”