Bay Area weather: Rain, gusty winds and snow on local peaks expected for much of this week

The warm, sunny weather this past weekend might have lulled some Bay Area residents into believing that the winter rainy season is over.

But it’s back to reality this week. A series of storms from the Pacific Northwest will bring steady rain, gusty winds and even snow on the tops of some of the Bay Area’s highest peaks, forecasters said Monday.

The first storm will sweep in late Tuesday into Wednesday morning, with another on Friday, and after a brief respite on Saturday, another expected Sunday and Monday. Despite a few minor events this month so far, Wednesday’s rain is expected to be the first significant rainfall in the Bay Area in four weeks, since Feb. 13.

“It will be a little bit more rain than we have seen for a while,” said Jan Null, a meteorologist with Golden Gate Weather Services in Half Moon Bay. “We’ve had a zig-zag line all the way through this winter — a wet period in November, then an extended dry period, then back up. We’ll probably end up with pretty much normal rainfall for the season.”

Altogether, forecasters expect 1 to 2 inches through this weekend in most Bay Area cities, with 4 inches or more in the North Bay Hills, Santa Cruz Mountains and Big Sur.

Those amounts should bring rain totals to close or nearly close to historical averages in many places. San Francisco on Monday was at 97% of its historical rainfall average for March 10, with San Jose at 70%. The East Bay has been lagging, with Oakland at 56% of normal.

The Wednesday rain event in the Bay Area is a weak atmospheric river, according to the Center for Western Weather and Water Extremes at UC San Diego. It is forecast to be a 1 on a scale of 1 to 5.

The biggest impact of the incoming storm systems may be on the Sierra Nevada.

The National Weather Service is forecasting 1 to 3 feet of new snow across the Sierra, with up to 3 feet at the highest elevations around Lake Tahoe.

“It’s a little bit of a Miracle March,” said Courtney Carpenter, a meteorologist with the National Weather Service in Sacramento. “It’s good news for our Sierra snowpack.”

On Monday, the statewide Sierra snowpack, which provides nearly one-third of California’s water supply, was at 81% of its historical average. Snowfall this winter has been greater in the north. The Northern Sierra, whose watersheds flow to many of the state’s largest reservoirs, on Monday had a snowpack 97% of its historical average. The Central Sierra snowpack was at 76%. And the Southern Sierra was at 75%.

“The storms are going to be colder so they are going to generate more snow than other storms,” Null said. “One inch of water from a warm storm might give you 4 to 6 inches of snow. But with a cold storm coming from the Pacific Northwest you might get a foot of snow from an inch of water.”

Forecasters said travel, particularly on Wednesday and Thursday, will be difficult in the mountains. There could well be low visibility, snow accumulating on highways, and chain controls, they said.

Winds could be up to 60 mph Wednesday at Sierra mountain passes.

“When you combine that with the heavy snow, there’s going to be some nasty travel conditions,” Carpenter said.

The National Weather Service issued a winter storm watch from 10 pm Tuesday through 10 pm Thursday.

The Bay Area might see some snow also.

Forecasters said the snow level Wednesday and Thursday could drop to 3,000 feet in the Bay Area. That would mean light snow on the top of Mount Saint Helena (4,341 feet) in Sonoma and Napa counties; Mount Hamilton (4,213 feet) in Santa Clara County; and Mount Diablo (3,848 feet) in Contra Costa County.

The rain in modest amounts is a good thing for water supply and fire risk. But there is a down side.

“These are moderate storms. There’s nothing really heavy or really long lasting about them,” Null said. “But they will probably obscure the lunar eclipse at midnight Thursday.”