Hundreds of lightning strikes, thunder and downpours greeted Bay Area commuters Monday evening after an unexpected wind storm ripped through the region earlier in the day.
Earlier, powerful winds unexpectedly swept through the South Bay and up the San Mateo County coast, felling trees and knocking out power to thousands of residents.
The winds were generated by an “outflow boundary,” a meteorological phenomenon in which a weakening thunderstorm “breathes out” cool and moist air, according to an analysis by Drew Peterson, a meteorologist with the National Weather Service in Monterey.
Outflow boundaries are known for producing “gust fronts,” which is what the region experienced.
“These outflow boundaries are somewhat rare for our area, primarily because we just don’t see very many thunderstorms capable of generating (them),” Peterson wrote in his analysis.
The thunderstorms, which moved through the Monterey Peninsula into the Bay Area on Monday, are the product of a system centered several hundred miles west of San Luis Obispo, said Will Pi, a meteorologist with the weather service. More than 800 lightning strikes and cloud flashes were reported in the regions between noon and 5 p.m., according to the weather service.
The unsettled weather is expected to continue through Tuesday, with some locations getting up to a tenth of an inch of rain.
Monday’s strong winds were first reported in the Monterey area at about 2 a.m., with gusts up to 54 mph reported at Pebble Beach, said Carolina Walbrun, a meteorologist with the weather service.
They moved north throughout the morning, with gusts up to 54 mph reported at the Spring Valley weather station, located about halfway between Half Moon Bay and San Francisco International Airport.
“It wasn’t something we were expecting to occur,” said Brian Garcia, a meteorologist with the weather service. “Nothing in our data suggested there would be significant wind gusts out of this.”
In Santa Clara County, there were multiple reports of wires down, including locations in San Jose, Campbell, Los Gatos, Los Altos, Saratoga, and Cupertino. Santa Clara County Fire Capt. Bill Murphy said his agency responded to more than 20 calls related to wires down and pole fires between 2:30 and 4:30 a.m. The majority were in Los Gatos and Campbell.
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Pacific Gas & Electric Co. experienced several wind-related outages in the South Bay between 2:30 and 3 a.m., said Tamar Sarkissian, a spokeswoman for the utility. About 11,000 customers lost power. As of 3:30 p.m., power had been restored to all but 274 customers.
Sarkissian said the utility expected to restore power to all its customers by Monday night.
“It’s been an all hands on deck situation,” said Sarkissian, adding that PG&E brought in crews from other areas.
