Wildfire risks in California increase due to upcoming heat dome

Another bout of dangerous triple-digit heat is headed to much of inland California this weekend, creating new concerns for firefighters battling wildfires across the state, including two that have surpassed 15,000 acres.

“Friday will begin a pretty dramatic warm-up with a big, warm high in the middle of the day. [country] expanding westward,” the National Weather Service wrote in its Wednesday morning forecast. The upper-level high pressure ridge, known colloquially as a heat dome, will most directly affect the deserts of the San Joaquin Valley and Southern California, but nearly all of the Golden State can expect high temperatures this weekend.

The Los Angeles area will remain on the western edge of the system as it moves through the southwest before expanding north and west, creating significant “compressive heating” beneath the high-pressure ridge, said meteorologist Joe Sirard. from the weather service in Oxnard. Sirard said “heat dome” is not a precise meteorological term, but it describes the process that raises temperatures as air sinks below the upper ridge.

“That will help generate heat,” Sirard said. “The hottest weather should occur in the deserts, the San Joaquin Valley and inland valleys, away from the coast.”

Much of inland California is expected to experience moderate to significant heat risks on Friday, Saturday and Sunday, and in some areas at least through Tuesday. The San Joaquin Valley and Sierra Nevada foothills are expecting “dangerously hot conditions,” and an excessive heat advisory will go into effect Saturday through at least Monday, when temperatures as high as 110 degrees are possible.

In the south, Saturday is expected to be the warmest day, when highs in the valleys of Los Angeles County will reach 90 degrees, while deserts and low mountains will reach a high near 105 degrees.

Temperatures will be “a few degrees above normal for the most part through Wednesday of next week,” Sirard said. Coasts, however, will be largely unaffected as the upper ridge remains further east and the system could strengthen the marine layer over the weekend.

The high temperatures are already on firefighters' radar, coming just days after strong winds fueled the flames of the Post Fire, which began Saturday near Gorman in northern Los Angeles County and quickly exploded in size. .

“Any time the weather warms … it's obviously going to be a driving force for fire spread,” said Jonathan Torres, spokesman for the Los Angeles County Fire Department. “Obviously, this makes it much more difficult for handheld teams.”

As of Wednesday morning, the Post Fire was 39% contained and appeared to remain at 15,690 acres, according to fire officials. After days of treacherous red flag conditions (gusty winds and low humidity), firefighters were able to make “significant progress” Tuesday night, according to a Wednesday morning update.

“Last night's weather conditions were favorable and allowed crews to increase containment lines,” the update said, noting that a “significant warming trend” is expected to begin Thursday through the weekend. Winds were expected to reach 20 mph on Wednesday, far from negligible, but dramatically weaker than what crews had faced in recent days.

Due to the treacherous conditions and steep terrain, firefighters continued ferrying crews by boat across Pyramid Lake to more directly access the flames Wednesday as aerial crews continued to work from above.

In northern Colusa County, the Sites Fire had grown to 15,565 acres by Wednesday morning, nearly matching the size of the Post Fire, which recently became the state's largest wildfire of the year. The Sites fire was only 5% contained, according to the California Department of Forestry and Fire Protection.

Firefighters hoped to make significant progress Wednesday and Thursday, during a respite between strong winds that have mostly subsided and high temperatures on the horizon.

“It's going to be pretty hot this weekend, over 100 degrees probably for a four or five day period,” Cal Fire Sonoma-Lake-Napa Unit Chief Mark Marcucci told crews at the morning briefing. about Sites fires. “So what I'm asking you today is to continue that good work and let's see what we can do to minimize the number of people we need to have there over the weekend.”

Communities near the Post and Sites fires remained under evacuation orders, and dozens of buildings were still threatened.

Statewide, there were at least two other major wildfires still active: the Point Fire in Sonoma County, which was 50% contained as of Wednesday and had burned 1,207 acres, and the Aero Fire in Calaveras County , which grew to 5,425 acres on Wednesday and was 33% contained, according to Cal Fire.

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