EM – The red flag warning hit much of the Bay Area as the dry lightning threat approaches


Concerns about dry lightning and the potential for more catastrophic forest fires lurked across the Bay Area on Thursday, adding to concerns that already gripped the region amid a terrible fire season.

The culprit was a monsoon-like system that was running out rose in the southwestern United States.

“We have this strong southerly current entering the area,” said meteorologist Gerry Diaz. “It’s that monsoon humidity.”

According to forecasters, monsoon humidity rises high into the atmosphere, propelled by the hot air rising over the desert. The hot air then eventually meets cold air higher in the atmosphere to create stormy conditions, including thunder and lightning.

Precipitation is produced, but the Bay Area’s hot and dry conditions are common to late summer and early Autumn is typical, often prevent raindrops from reaching the surface, said Diaz.

The danger of dry lightning and the possibility of strong gusts of wind prompted the weather service to issue a red flag warning from 5 p.m. Thursday to Friday 11 a.m. The East Bay Hills and the Interior Valley were affected by the warning, as were the Diablo Range and the North Bay Mountains.

The latest heat wave was also the occasion for the state’s independent system operator, a Flex warning from 4:00 p.m. to save energy. until 9 p.m. On Wednesday, he urged consumers to reduce their energy consumption in order to relieve the power grid. On Wednesday afternoon, the agency issued another Flex Alert for the same period Thursday.

“This is the timeframe that we expect the most likely to be,” said Diaz. “Just enough moisture moves north to interact with the environment. When it arrives, it will begin in parts of North Bay in northern Sonoma and Napa counties. If it hangs around long enough, you can see it in the East Bay. ”

A widespread lightning storm could affect the fight to contain California’s two largest forest fires. According to the California Department of Forestry and Fire Protection, the Dixie fire burned 922,192 acres and was 59% contained on Tuesday morning. The Caldor Fire had burned 217,569 acres and was contained 50%.

According to Cal Fire forecasters, hot and dry conditions were expected to continue around the Dixie Fire in Counties Butte, Tehama, Plumas, Shasta, and Lassen to rule. On Thursday night there was little danger of thunder and lightning.

In El Dorado County, according to Cal Fire, higher temperatures and strong winds threatened fire activity, as did the possibility of lightning strikes.

Weather and climate expert Daniel Swain wrote on social media that the incoming weather at this time was similar to thunderstorms in previous years. Both the August Complex and CZU Lightning Complex fires last year were fueled by thousands of lightning strikes across Northern California.

NorCal’s Thu / Fri weather setting is reminiscent of previous thunderstorms in September. The main components include the & medium subtropical moisture tap offshore low pressure system. Very light showers possible, but the main problem remains dry (or almost so) lightning. #CAfire #CAwx pic.twitter.com/dKmF3U082d

The August Complex Fire burned 1,033 million acres – making it the largest forest fire in California history – destroyed 935 buildings and killed a firefighter. The CZU Lightning Complex Fires in the San Mateo and Santa Cruz counties burned 86,509 acres, destroyed 1,490 buildings, and killed one person for 36 days.

Diaz said the system on the way was nowhere near as powerful as those that started the fires in 2020 and won’t have nearly the same lightning activity.

“Essentially, this system and its interaction with the environment were much stronger,” said Diaz. “The good news for this event is that we don’t have anywhere near the strength or volatility. It’s a lot less pronounced. ”

The heat would stay strong, said Diaz. Temperatures were expected to top 100 degrees again on Wednesday at common hotspots like Brentwood, Concord, Livermore and Walnut Creek, and they should also hit 95 in areas of the Santa Clara Valley and 90 in downtown San Jose

Thursday these numbers were expected to drop 7-10 degrees in South Bay and 10-15 degrees across the region. Diaz said those temperature drops would just as quickly be replaced by higher humidity and muggy, sticky conditions.

“It gets muggy in the period before the storms,” ​​he said. “It’s very common on the east coast. When the cold front hits it gets very humid, and after the storm passes, the system behind it is much colder, much drier. ”

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The cool down is expected to arrive on Friday morning as the monsoon moisture disappears, he said.


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