Collapsing thunderstorms cause bizarre isolated winds that whip San Francisco Bay Area The gusts knocked some communities while others areas were completely still

Story update Monday, 3 p.m.: Meteorologist Jan Null of Golden Gate Weather Services says Monday's early morning winds were the result of collapsing thunderstorms. As storm cells moved from Southern California into Monterey County, air rose into the lower atmosphere. During the nighttime hours as temperatures cooled, the convective heating process that supports the air in the lower atmosphere stopped and the air fell to the ground.

"As you get into the nighttime hours and you don't have that lift to maintain all that air at the top of the thunderstorm, then the primary force is gravity," Null says. "This heavy air is going to be coming down to the earth and it spreads out like an upside down mushroom."



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Meteorologists are baffled by strong wind gusts that ripped through concentrated pockets of the Bay Area early Monday morning, while other areas remained completely still.

The National Weather Service reports that a gust of 54 mph roared through Pebble Beach at 2:30 a.m., while only 10 minutes away in Monterey conditions remained completely calm.

"We had a very unusual event happen overnight," says Charles Bell, a meteorologist with the National Weather Service Bay Area. "We had isolated strong periods of winds. It's really remarkable. Usually wind storms are more widespread, while this wind occurred in concentrated pockets."

The first gusts roared through Pebble Beach and the southwesterly winds traveled north reaching up to 40 mph in Santa Cruz, up to 37 mph in Los Gatos and at the San Jose Airport.

The weather service recorded the last gust from the event at 3:30 a.m.; it was a 35 mph wind at the Golden Gate Bridge. Bell says there are anecdotal reports of high winds in parts of Marin.

"We left our window open because of heat and winds were so strong our interior doors were slamming shut and flying open!" Thais Derich of Mill Valley wrote on Facebook.

The winds knocked down trees and power lines. PG&E reported 11,000 customers without power at one point.

The event lasted about two hours.

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Unusual weather around California in September 2017. Unusual weather around California in September 2017. Photo: Courtesy Photo: Courtesy Image 1 of / 15 Caption Close Collapsing thunderstorms cause bizarre isolated winds that whip San Francisco Bay Area 1 / 15 Back to Gallery

The windy conditions weren't in the forecast and came as a surprise to Bay Area residents.

"There was no indication of this happening today," Bell says. "We have computer models that are very high resolution that pick up a lot of features in the atmosphere and they didn't detect it. We're going to look through the data to find out what caused it."

He added: "This is a very unusual situation. And one we wish we'd given people more of a heads-up on. It definitely was not forecast."

Bell says one of the office's senior scientists will be analyzing data today to determine the source of the wind.

"One idea that's been kicked around is there's a storm swell to the south and potentially some energy came up from that," he says.

While the windy conditions are over throughout the Bay Area, the National Weather Service says thunderstorms are in the forecast for later today. There's a 30 percent chance of rain and thunderstorms in San Francisco and those showers could arrive as early as 3 p.m.