Deadly ‘bomb cyclone’ storm slams California, toppling trees and causing blackouts

Tribune Content Agency

LOS ANGELES — At least one person was killed as a wet and windy storm arrived in California on Tuesday, delivering more rain, snow and hazards to residents of the Golden State on the second day of spring.

The person, who has not been identified, was killed when a tree fell onto a vehicle on Alpine Road in Portola Valley, according to the California Highway Patrol.

The death was reported as the low-pressure system rocked the Central Coast, where widespread rain and damaging wind gusts also snarled traffic, knocked glass out of skyscrapers and left tens of thousands without power.

The storm came in “much stronger than expected,” particularly in the southern half of the San Francisco Bay and Monterey Bay areas, UCLA climate scientist Daniel Swain said in a briefing Tuesday. He said the system had reached the benchmark for a phenomenon known as bombogenesis, or a “bomb cyclone,” which indicates a rapid drop in pressure.

Unlike an earlier bomb cyclone this winter — which occurred about 100 miles southwest of San Francisco — “this is very close to the coast,” Swain said. “So the impacts are actually more immediate and greater than they were back then.”

The National Weather Service has issued high wind warnings from San Francisco to San Diego, as well as inland areas, including Palmdale, Lancaster and the Antelope Valley.

Heavy rain is likely to lead to rapid runoff and areas of flooding as the storm moves south Tuesday. Heavy snow will pose hazards in the mountains of Southern California as well as the central and southern Sierra Nevada, where up to 4 feet could accumulate at higher elevations.

Although rain and flooding were concerns in the San Francisco Bay Area, “mostly it’s the wind with this system,” said Rick Canepa, a National Weather Service meteorologist in Monterey County.

“The winds have really ramped up quite significantly because we’re dealing with not just one low-pressure center, but at least two and possibly a third one that are just kind of rotating around each other,” he said.

The rare occurrence, known as the Fujiwhara effect, has contributed to peak wind gusts “upward of 60 to 75 mph in the Santa Cruz Mountains,” Canepa said, with strong 50- to 60-mph winds across Santa Cruz and Santa Clara counties.

Up and down the San Francisco Peninsula, high winds and heavy rains were flooding streets, knocking down trees and causing power outages — just a week after a similar, high-intensity storm rocked the generally weather-placid area.

Visibility was minimal on Interstate 280, which follows the peninsula from San Francisco to San Jose. Ferocious gales blew rain horizontally across the freeway, turning the high-speed interstate into a slow-motion crawl.

In Menlo Park, trees were toppled across small side streets and major arteries such as Santa Cruz Avenue, where a crew was summoned to chainsaw a 60-foot cedar that had been uprooted and was blocking two lanes of traffic. The city’s high school lost power, prompting teens to call their parents to see whether the lights were on at their homes.

By Tuesday afternoon, about 150,000 Californians were without power, primarily in Santa Clara, Alameda, Santa Cruz and San Mateo counties, according to outage trackers.

David King, a meteorologist at the weather service in Monterey, said the storm could develop a “sting jet,” or a localized acceleration of winds next to a center of low pressure, which could result in particularly severe wind near Monterey Bay.

“The lower pressure is directly west of Santa Cruz County out over the ocean, and so if a sting jet develops, it would likely be impacting our area,” he said. Even without such a development, winds are expected to remain strong throughout the day.

“There’s a reason why the Santa Cruz County-San Mateo coastline, as well as Monterey County, are all under a high-wind warning, because we’re expecting these strong winds directly near the center of low pressure,” King said.

The cold system was expected to gain some subtropical moisture as it moved toward Southern California — a recipe for heavy rain. Flood watches and advisories were in effect across the region, and roadway flooding and traffic jams were reported in Los Angeles.

High temperatures in Southern California were likely to drop into the 50s — about 10 to 15 degrees below normal for this time of year, said David Sweet, a weather service meteorologist in Oxnard.

“There could be some excessive rain when the strongest part of the storm moves through, so we’ll be concerned with flooding,” Sweet said. “We’re also going to be concerned with strong winds. Winds are really picking up in the coastal waters now — they’re seeing gusts on the order of 40 and 50 mph — so it looks like the storm’s going to deliver on the winds.”

In the Los Angeles area, up to 3 inches of rain is possible along the coast and in the valleys, and up to 5 inches in the foothills, Sweet said.

By midday, flooding and debris flows had spurred road closures along sections of the 5 Freeway in Anaheim, Santa Ana and near Elysian Park in L.A., as well as Pacific Coast Highway in Huntington Beach and Dana Point, according to Caltrans.

Weather conditions also led to the closure of several roads in the Angeles National Forest, including portions of Highways 2 and 39, with no estimated time of reopening.

A brief break in the rain around Los Angeles was expected to “destabilize the atmosphere and increase heavier showers and thunderstorms coverage” later Tuesday, the weather service said.

The storm arrives after a season of wet and destructive weather, including a series of nine back-to-back atmospheric river storms in January, which contributed to the deaths of nearly two dozen people.

In late February and early March, historic snowstorms dropped fresh powder at elevations as low as 1,000 feet — including at the Hollywood sign — and trapped residents under several feet of snow in the San Bernardino Mountains, where at least 13 people died.

More storms in recent weeks brought levee breaches and devastating floods, including in Pajaro and in Tulare County communities near the Tule River, both of which endured evacuations and widespread property damage as floodwaters streamed from swollen rivers.

Thousands of residents in Tulare remained under evacuation orders Tuesday, including the areas of Alpaugh and Allensworth and portions of Porterville along the Tule River, where officials continued to be concerned about rising river levels as they released water from Lake Success to make room for incoming flows.

The lake was at about 96% of capacity, and officials were “continuing a high output to get it lower in anticipation of today’s rainfall and future snowmelt,” said Daniel Potter, a spokesman with the California Department of Forestry and Fire Protection, or Cal Fire, which is assisting with emergency operations and flood response.

Hundreds of small levee breaks have been reported, including a breach that sent floodwaters onto properties near Allensworth. At least seven structures have been destroyed, more than 652 have sustained major damage and 177 took minor damage. Nearly 24,000 structures remain threatened, according to Cal Fire.

Multiple small breaks have been temporarily repaired with “super sacks,” or bags of sand and rocks, Potter said. “We’re keeping an eye on some other areas, but as of right now, everything is looking good — we’re maintaining right now,” he said.

Tulare County Emergency Operations spokeswoman Carrie Monteiro said the county was vulnerable to flooding in part because of the severe drought that has gripped the region for more than a decade.

“And so our waterways had not been tested with this kind of water — the water that is going through them right now,” she said. “So we’re preparing for the next storm. We’re preparing to have tools and the resources we need on the ground. And ready to go in a significant way.”

The storm was also expected to bring up to 3 inches of rainfall in Orange County and the Inland Empire and up to 8 inches in the San Bernardino Mountains, along with higher-elevation snow.

“It’s a high amount of rain — the storm is a really strong one,” said Casey Oswant, a meteorologist at the weather service in San Diego. She added that strong winds from the south could produce a lot of rain over the mountains.

Such winds are uncommon for the region, which typically sees winds from the west, northwest or southeast, said Jonathan Porter, chief meteorologist at Accuweather.

When damaging winds originate from uncommon directions, it increases the risk of toppling trees because many root systems “build up” over time to support more typical wind directions, Porter said. That’s especially concerning given how saturated the ground is from recent rainfalls, which can also make trees more susceptible to falling.

The confluence of factors — including the bomb cyclone, Fujiwhara effect and sting jet — is remarkable, said Swain, the UCLA scientist.

“The storm is really raking Santa Cruz and San Mateo counties in particular,” he said as he reviewed radar images. “I have never seen anything quite like it.”

Conditions are expected to clear in most of the state Thursday into Sunday, forecasters said. But yet another storm could arrive as early as next week.