On Saturday, as a powerful winter storm headed toward the Bay Area, San Francisco residents received a tornado warning from the National Weather Service. But no tornado touched down. Yet 50 miles to the south, Scotts Valley, in Santa Cruz County, didn’t receive a tornado warning and a tornado did hit the community, flipping seven cars, breaking trees and causing five injuries.

What happened?

Despite computer models, radar systems and modern satellites, the event highlighted how predicting the precise location of extreme weather events still can be difficult, experts said Monday.

Officials from the National Weather Service said conditions in San Francisco and Santa Cruz County were very similar Saturday. The storms came from the same system. Radar images showed similar patterns. And the winds turned out to be similar — with gusts to 80 mph toppling trees at Golden Gate Park in San Francisco and the tornado in Scotts Valley later in the day reaching 90 mph.

The tornado never touched down in San Francisco. But the conditions in the atmosphere with wind speed and direction were right, said Brian Garcia, warning coordination meteorologist for National Weather Service in the Bay Area.

“San Francisco got lucky,” he said.

The National Weather Service issued a tornado warning for San Francisco at 5:51 a.m. Saturday, the first in its history.

Tornadoes are rare but not unheard of in California. Since 1950, there have been 482, according to federal records. The Central Valley receives more than other areas. The Bay Area’s most recent was in 2016, when a waterspout appeared during a storm over Lake Berryessa in Napa County. The East Bay had one in Brentwood in 2010. Gilroy had one in 2007.

Santa Cruz County has had 7 in the past 75 years: The most recent occurred Jan. 6, 2019, when one tore much of the roof off the Dolphin Restaurant at the end of the Santa Cruz Wharf before dissipating. Often they form just a few miles offshore as waterspouts, giving little warning.

“These things have very short life spans,” said Jan Null, a meteorologist with Golden Gate Weather Services in Half Moon Bay. “It’s not like you can track it for hours. That makes them very tough to warn people about.”

Tornadoes are less likely to occur in mountainous areas like Santa Cruz County, than in flat areas, because mountains often break up the swirling wind patterns. Given that, and seeing no tornado touch down in San Francisco, Garcia said, the National Weather Service issued a severe thunderstorm warning for Scotts Valley and much of Santa Cruz County instead of a tornado warning at 1:25 p.m. as the storm’s impacts moved south.

“A severe thunderstorm warning and a tornado warning both have similar calls to action,” he said. “Seek shelter immediately. Severe thunderstorms can have winds as strong as tornadoes. The difference is they are in a straight line rather than spinning.”

Another difference is the type of notification the public receives.

Under federal rules established in 2012, the National Weather Service sends alerts to cell phones of people living in the affected area when there are tornado warnings, along with other threats like hurricanes or tsunamis.

But in 2021 after getting complaints of too many cell phone alerts from residents in the Midwest where such storms are more common, the agency decided to only send them for the most extreme types of severe thunderstorms. There are three levels, and the agency’s meteorologists determined that Saturday’s  storm looked like the lowest of the three.

As a result, 1 million people in San Francisco had an alert from the federal Weather Emergency Alert service buzz their phones Saturday morning. Nobody in Scotts Valley did, although some people reported phone warnings which likely came from weather apps and other programs.

“We had a front-row seat,” said Denise Fritsch, a saleswoman at Home by Zinnia’s decor store on Mount Hermon Road next to Target, where the damage was worst. “Our doors were sucked open, then slammed shut really quick. The wreaths went sailing.”

A few blocks away, the funnel cloud hit her husband’s car, breaking a window, mirror and tail light but leaving him unhurt, Fritsch said.

“If anybody knew it was coming they should’ve warned us,” she said, “but I don’t know if anyone knew what was coming.”

Bellina Jones, 21, a shift lead at The Penny Ice Creamery nearby, got wind warnings on her phone. She was in the back of the shop washing a blender and came to the front as a customer said, “Tornado, get down!” Jones said she would have liked to receive a tornado warning on her phone, but noted the incident was very unusual.

“I get why nobody would think to do that here,” she added.

Power was back on Sunday, and by late Monday all 15 traffic lights that had been blown down were expected to be back up, said Scotts Valley Vice Mayor Derek Timm. The main damage was to Scotts Valley Middle School where a fallen tree wrecked several classrooms, he said.

“There’s still branches down, trees snapped off and ripped apart,” he said. “But our businesses have reopened. Some lost thousands of dollars. It’s the holiday season. It would be wonderful if the greater community could help them out.”

The Scotts Valley tornado was relatively small. It was just 30 yards wide and lasted 5 minutes, from 1:39 p.m. to 1:44 p.m, according to the National Weather Service preliminary report. On a  scale of 0 to 5, it was a 1.

But Garcia of the National Weather Service said he and other agency officials will evaluate to see if there’s anything they should do differently in the future. The agency might want to consider increasing phone alerts for severe thunderstorms in California, said Null, of Golden Gate Weather Services.

“You have to pull the trigger sometimes not knowing if it is going to verify,” Null said, citing the tsunami warning two weeks ago after a major earthquake 40 miles off the Humboldt County coast. “You can quibble about the details after the fact. But it’s a much better mode of operation to be safe than sorry.”

Bay Area News Group reporter Nollyanne Delacruz contributed to this story.

Originally Published: December 16, 2024 at 3:27 PM PST