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A day of wild weather in California: the Fujiwhara effect, a bomb cyclone and a landspout warning


Even after an unusual winter of heavy rain, wind and snow, the storm that hit California on Tuesday arrived with some surprising conditions.

The storm was marked by strong winds in the Bay Area and other parts of central and northern California that downed trees, created treacherous travel conditions, smashed windows in downtown San Francisco and caused power outages. The National Weather Service issued high wind warnings for a stretch of the coast from San Francisco to San Diego, as well as inland areas, including Palmdale, Lancaster and the Antelope Valley.

fujiwhara effect

On Tuesday afternoon, as the storm approached the Bay Area, the system developed two “eyes,” or areas of low pressure, resulting in a “double whammy” for San Francisco and Santa Cruz, said Brian, a meteorologist. from the Bay Area National Weather Service. Garcia.

The rare occurrence, known as the Fujiwhara effect, intensified the winds as areas of low pressure danced around each other.

Rick Canepa, a National Weather Service meteorologist in Monterey County, cited the two centers of low pressure “and possibly a third that circle around each other.”

The phenomenon was contributing to peak gusts of 60 to 75 mph in the Santa Cruz Mountains, Canepa said, with winds of 50 to 60 mph in Santa Cruz and Santa Clara counties.

cyclone bomb

UCLA climatologist Daniel Swain noted other unusual attributes of the weather system, including a “sting jet,” or localized acceleration of the winds next to a center of low pressure.

“The name comes from the 3D visualizations of this feature,” he said, “which looks a bit like a scorpion’s tail coming down from the sky.”

Swain told a briefing Tuesday that the system had reached the bombogenesis reference point, or “bomb cyclone,” indicating a rapid drop in pressure.

Unlike a previous bomb cyclone this winter about 1,000 miles southwest of San Francisco, this one “is very close to shore,” Swain said. “So the impacts are actually more immediate and bigger than they were back then.

“The storm is really hitting Santa Cruz and San Mateo counties in particular,” he added as he reviewed the radar images. “I had never seen anything like it”.

southern california winds

Conditions weren’t too bad in Southern California, which recorded steady rain Tuesday, with more rain scheduled for Wednesday.

The winds were strong from the south, unusual in the region, where they typically come from the west, northwest or southeast, said Jonathan Porter, Accuweather’s chief meteorologist.

When winds originate from unusual directions, the risk of downing trees increases, because root systems “build up” over time in response to more typical patterns, Porter said. That’s especially concerning given how saturated the ground is from recent rains, another factor that can make trees susceptible to toppling.

groundspout warning

the weather service issued special statements covering large swaths of Ventura and Los Angeles counties, citing the potential for pea-sized hail and the possibility of landspouts through Tuesday afternoon.

Waterspouts are similar to tornadoes, but the funnel’s circulation begins at ground level and rises to become towering cumulus clouds, according to the National Oceanic and Atmospheric Administration.

It is not clear if any developed.

Times staff writers Luke Money and Christian Martinez contributed to this report.

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