Atmospheric river storm: When it’s arriving and which areas will be hit hardest

The atmospheric river storm steaming toward Northern California from Hawaii is likely to bring the wettest conditions the Bay Area has seen in two months.

The storm is on track to hit the North Bay by mid-morning Thursday, spreading across the Bay Area by Thursday afternoon, with the heaviest winds, rainfall amounts and disruption — from power outages to flooded roadways — on Thursday night into Friday morning, forecasters said late Wednesday.

“This will be similar to what we saw in January,” said Brayden Murdock, a meteorologist with the National Weather Service in Monterey, who predicted winds up to 50 mph in many areas. “Not as strong as the biggest one of those nine atmospheric river storms in January, but on the same level. Plenty of wind. Strong rain. And chances of rain through the weekend.”

The storm is expected to be a category 3 atmospheric river event, perhaps a category 4 in the Big Sur area, on a scale of 1-5, with 5 being the highest, according to scientists at the Scripps Institution of Oceanography in San Diego.

CW3E AR Update: Warm #AtmosphericRiver to Bring Heavy Precipitation, Potential Flooding to California Later This Week.

Read more about this AR and the potential impacts of the storm on our website: https://t.co/8Glswmwqvq pic.twitter.com/evXX5kaZnH

— CW3E Scripps (@CW3E_Scripps) March 7, 2023

Cities around the bay are expected to receive about 2 inches of rain from Thursday morning to Friday night, with San Jose forecast for about 1.5 inches, the National Weather Service estimated. The East Bay Hills could receive 3 or 4 inches, and the North Bay Hills and Santa Cruz Mountains are likely to be soaked with 6 to 8 inches. In Big Sur, an astounding 14 inches of rain is forecast from the storm, Murdock said.

With the potential of Highway 1 being washed out again due to huge mudslides, Monterey County emergency officials on Wednesday urged Big Sur residents to stockpile at least 2 weeks of essential supplies.

Although the rain will be heavy, there haven’t been huge storms in recent days, so no major rivers or creeks in the Bay Area were forecast as of Wednesday to go over their flood stage levels. A few, like the Russian River at Guerneville, were expected to come close, then recede Saturday and Sunday.

In the Santa Cruz Mountains, where power outages and downed trees have been common all winter, locals took it in stride.

“People are buying generators, tarps, gas cans and chainsaws,” said Lance Lollis, a manager at Scarborough Home Center in Ben Lomond. “It’s like ‘Here we go again.’”

Lollis said that residents can ride it out.

“This is round 10,” he joked, referring to the number of atmospheric river storms this year. “But we’re up here for a reason. You either become mountain folk or you leave.”

For most Bay Area residents at lower elevations, power outages, flooded roadways and downed trees were a possibility.

“Rain, winds and flood risk are a bad combination,” said Mayra Tostado, a PG&E spokeswoman. “They can cause trees falling into our power lines.”

Tostado said that PG&E is pre-positioning repair crews in areas where outages are most likely, including Peninsula hills and South Bay hills. She said it was possible that the Bay Area could see outages of 100,000 customers, depending on the strength of the storm.

The Santa Clara Valley Water District had crews out Wednesday clearing debris from creeks to reduce flood risk, and it continued to maintain sandbag stations for residents who live near flood-prone areas.

“We’re keeping a close eye on the storm,” said Matt Keller, a spokesman for the district. “We don’t expect any major issues unless the rainfall amount increases significantly.”

The storms this year have all but ended California’s drought in many parts of the state, including the coastal counties, Bay Area and Sierra foothills. Parts of Southern California that depend on water from the depleted Colorado River, are in worse shape.

Gov. Gavin Newsom is expected to begin lifting his emergency drought declaration regionally starting in April.

This week in the Sierra, which already has received more snow this winter than any year since 1993, more blizzard conditions are a near certainty.

From Thursday to Sunday, 5 to 6 feet of new snow is expected at higher elevations like Tioga Pass, Sonora Pass, Ebbetts Pass and Carson Pass, the National Weather Service said, with 3 to 4 feet at Donner Summit. Interstate 80 and Highway 50 were likely to be closed again, as they have been regularly this winter.

How much snow has already fallen?

As of Wednesday, a stunning 603 inches — 50 feet — had fallen at the UC Central Sierra Snow Lab at Donner Summit since Oct. 1, with 18 feet of that falling since Feb. 22. Only four other winters since 1946, when the lab was built, have had more, according to lab manager Andrew Schwartz: 1952, 1983, 2011 and 1982.

To hit the all-time record of 812 inches, set in 1952, the Sierra will need to see another 17 feet this winter.

Some perspective on current snow depths at the lab. https://t.co/RaYsd1vzlU

— UC Berkeley Central Sierra Snow Lab (@UCB_CSSL) March 2, 2023

Because of the huge snowpack, there have been concerns that a warm atmospheric river storm could cause much of it to melt, triggering major flooding across the Central Valley. Experts have said in recent days that the deep snow can absorb rain from one big storm, but if more atmospheric rivers follow in succession next week, it could increase the risk.

“I don’t think it’s going to cause severe flooding,” said Daniel Swain, a climate scientist at UCLA, about Thursday’s storm. “It will most certainly cause some flooding, at least minor or moderate flooding. But I don’t think widespread severe flooding.”

He noted that residents of the Sierra Nevada and other mountain areas — some of whom moved up there during the COVID pandemic — have faced wildfires, droughts, and now extreme winter conditions.

“A lot of folks who live at those elevations are burned out,” Swain said. “And folks at the weather service and emergency managers are burned out. It’s been one thing after another.”

CURRENT CONDITIONS (3/08/23 9:05am)

•I-80 is R2 in both directions from the Nevada state line to Applegate.
• SR-267 is R2 from Northstar to Kings Beach.
• SR-89 is R2 from Truckee to Tahoe City.
• SR-28 is R2 from Tahoe City to Kings Beach. pic.twitter.com/Sox52c8DDt

— CHP Truckee (@CHP_Truckee) March 8, 2023