SAN JOSE, Calif. — Across the San Francisco Bay Area, public safety workers and weather experts figured there wasn’t much they hadn’t seen during this relentless winter of atmospheric rivers, a freezing Alaskan Gulf jet stream, snow and nearly 100 mph winds.
But after Tuesday’s ferocious storm, which surprised forecasters and set new records, they had a change of heart.
“I’m a scientist. I tend to not be a fan of flamboyant adjectives,” National Weather Service meteorologist Warren Blier said Wednesday. “But after the winter we’ve had, to get something like yesterday, I thought it was extraordinary.”
And not in a good sense. The destructive, deadly and ultimately rare “bomb cyclone” that touched down in the region killed three people. Falling trees killed a homeless man in Oakland near Lake Merritt, an elderly man sitting in a car in the Walnut Creek community of Rossmoor, and a man driving a truck in Portola Valley.
The storm also caused a barge to slam into Lefty O’Doul Bridge near Oracle Park in San Francisco, smashing railings and wooden decking. It sent glass from broken windows in the Salesforce Tower, Millennium Tower and other San Francisco skyscrapers crashing to the ground. It wrecked two lanes and a retaining wall on Interstate 580 in Livermore.
How did it happen?
Essentially, a swirling low pressure system, known to meteorologists as a “mesoscale cyclone”, passed over the Bay Area. It deepened quickly, increasing wind speed. Tuesday broke the all-time record for the lowest barometric pressure ever recorded in March at San Francisco International Airport.
The cold storm split into two swirling low-pressure zones next to each other. The rare phenomenon is known as the Fujiwhara Effect, for Sakuhei Fujiwhara, a Japanese meteorologist who discovered it in 1921. Normally, experts said Wednesday, the effect usually happens with hurricanes and tropical typhoons. Sometimes, it can be seen off the California coast, but rarely over land.
“I’ve watched a lot of weather. It’s rare that they make it to shore,” said Marty Ralph, director of the Center for Western Weather and Water Extremes at the University of California, San Diego. “It was very dramatic. The images over populated areas were dramatic. It was a very special case.”
The Fujiwhara Effect, however, didn’t cause the increased wind speeds. If anything, the swirling, dueling systems might have slowed the winds down, said Jan Null, a meteorologist with Golden Gate Weather Services in Half Moon Bay.
Supercomputer models that forecasters use predicted the center of the low pressure zone would be farther offshore. Instead, it arrived about 30 miles to the east, over the Peninsula, Santa Cruz Mountains, San Francisco and East Bay.
“There’s a lack of data over the ocean,” Null said. “That hinders what goes into the models. A tiny error can end up with a 30-mile difference. If the center of the low had been over the ocean, we would have had some rain, but less wind.”
Null said more buoys, weather balloons, and higher resolution data from satellites is needed to continue to improve forecasts.
“It all begins with the data,” he said. “You want the highest resolution you can get going into the forecast model and the biggest, fastest computer. All those things have dollar signs.”
By Wednesday afternoon, the rain had stopped.
At 1 p.m., the weather service reported 24-hour rainfall totals of more than 4 inches in Wunderlich Park in San Mateo County; 3 3/4 at Ben Lomond in Santa Cruz County and 2 inches in Los Gatos in Santa Clara County. About 1 3/4 inches fell in Orinda, the top spot in Contra Costa County; about 1 1/4 was recorded in downtown Oakland; and about nine-tenths fell in San Francisco.
Forecasters said dry weather is expected Thursday through Sunday, with another storm system possible next Monday.
“Things will dry out,” said Alexis Clouser, a meteorologist with the National Weather Service. “Enjoy it.”
Although the rain totals from the storm were not extreme, it was the explosive and violent wind that did the real damage. The wind toppled a big rig on the Bay Bridge, and churned up waters in the bay with gusts the weather service measured up to 81 mph.
In Contra Costa County, emergency crews responded to 100 calls over a 24-hour period, involving myriad incidents, said Contra Costa Fire Protection District spokesperson Steve Hill. Among them were downed wires, local small flooding and vehicle crashes.
In Santa Cruz County, the San Lorenzo Valley Unified School district canceled school for all five of its schools Wednesday, citing extensive damage from fallen trees and power lines throughout the Santa Cruz Mountains.
Highway 9, which links Santa Cruz to the South Bay and runs through the middle of Boulder Creek, was shut down in four spots due to weather-related traffic hazards Wednesday, according to the California Highway Patrol.
Pacific Gas and Electric Company was dealing with 67,557 customer power outages throughout the Bay Area at 3 p.m. Wednesday. — down from the peak of 234,000 customers without power at about 6:45 p.m. Tuesday.
The definition of a “bomb cyclone” is a storm where the barometric pressure falls at least 24 millibars in 24 hours. Tuesday, it fell that much in 17 hours at a buoy in the Monterey Bay. Blier, with the National Weather Service, said the unusual weather occurrences Tuesday happen about “once in every 10 years or rarer.”
But in the drought-busting winter of 2022-23 — which is bringing Sierra snow totals and some storms similar to conditions seen in famously wet years like 1997-98 and 1982-83 — Blier said California has been on a remarkable ride.
“Any other season, this would be the extraordinary, memorable event,” he said of Tuesday’s storm. “Now, this is like, top five.”
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(Mercury News staff writer John Woolfolk contributed to this report.)
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