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Update: Napa hits a record 110 degrees Sunday; fire-risk weather warning looms, along with possible power cuts

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Updated at 5:51 p.m. The ferocious peak of a Bay Area heat wave left Napa with record-tying heat on Sunday – and may force some residents to face pre-emptive power cuts amid a forecast of heat, dryness and increasing winds that may raise the risk of wildfires.

The National Weather Service reported a peak afternoon temperature of 110 degrees at Napa State Hospital, equaling the all-time record for the month. Napa last reached 110 on Sept. 7, 1904, and the previous high temperature on Sept. 6 was 106, also in 1904, according to Duane Dykema, a meteorologist at the weather service’s Monterey bureau.

No let-up in the extreme heat is expected on Labor Day, leading the weather service to announce a red flag warning for elevated fire risk from 10 p.m. Monday to 8 a.m. Wednesday in mountain areas of Napa County, Dykema said. The alert applies to areas above 1,000 feet in elevation.

An expected Labor Day high of 103 degrees contributed to the red flag warning, according to Dykema, along with the arrival of stronger winds late Monday night that may pull humidity below 10 percent by Tuesday morning.

In Napa, daytime winds Monday of 3 to 7 mph from the south-southwest are expected to increase to 7 to 17 mph from the south, with gusts reaching 22 mph, according to the weather service website.

Meanwhile, Pacific Gas & Electric announced that up to 103,000 customers across Napa and 16 other counties may face a power shutoff starting Monday evening. Notifications to potentially affected customers via text messages, email and automated phone calls began Saturday, about 48 hours ahead of a possible shutoff, and are expected to continue Sunday evening to provide about 24 hours’ notice, said PG&E spokesperson Katie Allen.

Besides unusually high temperatures, weather factors that may lead to a shutoff include humidity below 20 percent, as well as sustained winds above 25 mph and gusts of more than 45 mph, Allen said Sunday afternoon. Red flag warnings, the amount of flammable plant material and observation by PG&E field crews also factor into any decisions to disconnect service in a given area.

Shortly before 5:30 p.m. Sunday, PG&E customers in lost power Browns Valley and other pockets of west Napa, according to the utility’s online outage map. The number of customers affected and the cause of the outage were not immediately known.

Operators of California’s power grid also renewed an appeal to cut electrical use Sunday and Monday, even as energy consumption soars amid record-setting temperatures around the Bay Area and the state.

The California Independent System Operator issued a Flex Alert from 3 to 9 p.m. Sunday and again on Labor Day, asking the public to conserve as much as possible during the late afternoon and early evening in the hope of avoiding or at least lifting rolling power outages.

“With today’s excessive heat, increased electricity demand and wildfires taking out transmission lines, system energy supplies could be up to 4,000 megawatts short this evening,” CAISO said Sunday afternoon on Twitter.

No decisions affecting Napa County had been announced as of 5 p.m., according to Allen of PG&E. Utility companies would be given 10 minutes’ notice by CAISO to carry out such outages, which are not related to public safety shutoffs, she said.

Alameda Municipal Power, the provider for the city of Alameda, said a declaration of a Stage 3 emergency resulting in outages is “likely” in a message to customers Sunday. Marin Clean Energy issued a similar announcement Sunday and like other providers said California is in a “extreme heat storm.”

Gov. Gavin Newsom said the state is taking “aggressive” steps to free electrical capacity and reduce demand.

“California has always been the canary in the coal mine for climate change, and this weekend’s events only underscore that reality,” Newsom said in a statement. “Wildfires have caused system failures, while near-record energy demand is predicted as a multi-state heat wave hits the West Coast for the second time in a matter of weeks.”

Customers are asked to shift the bulk of energy use to late night or early daytime hours.

An excessive heat warning the weather service issued Saturday morning remains in force across the Bay Area until 9 p.m. Monday, with temperatures expected to exceed 110 in some interior areas – part of a heat wave that has raised renewed concerns about new wildfires and strained power supplies across California.

High temperatures in Napa are expected to reach triple digits on Monday for a third consecutive afternoon before easing to 98 on Tuesday and 90 Wednesday, the weather service said.

Saturday’s high temperature of 102 at Napa State Hospital exceeded the previous peak for Sept. 5 of 100, set in 2008, according to the weather service.

At noon Sunday, St. Helena and Calistoga opened air-conditioned spaces where residents could take refuge from the extreme heat.

The St. Helena cooling center opened inside the Carnegie Building at 1360 Oak Ave. and was open through 8 p.m. to those who cannot safely stay cool at home. Due to the coronavirus pandemic, various safety measures were in place at the center, including temperature checks, a requirement to wear a mask, and physical distancing between individuals and households, the city said in a news release.

Calistoga announced in a Nixle alert it opened a cooling center at the Community Center, 1307 Washington St., from noon to 8 p.m. on Sunday and will again Labor Day. Space will be limited due to social distancing requirements.

Officials urged people to conserve electricity to ease strain on the state’s power grid as the use of air conditioning soars amid triple-digit temperatures.

Steps customers can take include setting air conditioning thermostats to 78 degrees, if health permits; deferring use of major appliances; turning off unnecessary lights; unplugging devices not in use; closing blinds and drapes; using fans when possible; and limiting time the refrigerator door is open.

Fires have caused a generator and a solar farm to trip offline, further affecting the state’s power grid.

The extreme heat raises the risk of illness for those working or active outdoors, forecasters advised. Residents are asked to drink plenty of fluids, stay in air-conditioned spaces, avoid the sun, and check on relatives and neighbors. Children and animals should not be left unattended in vehicles under any circumstances.

Those who must work or spend time outside are asked to reschedule physical activity to early morning or evening, wear lightweight and loose-fitting clothing, and to know the signs of heat exhaustion and heat stroke.

Many recreational areas where Californians normally would celebrate Labor Day weekend or seek relief from summer heat were off-limits, including those surrounding Lake Berryessa in rural Napa County. The U.S. Bureau of Reclamation closed all day-use areas, boat launches, and concession-operated sites at the lake amid continuing mop-up of the Hennessey Fire, which erupted Aug. 17 and destroyed more than 300 homes in the county.

In San Francisco, parking lots at Ocean Beach were closed Sunday following a large gathering there on Saturday during what would have been the 34th Burning Man Festival, Mayor London Breed announced on her Facebook and Twitter accounts, expressing concern about the potential spread of COVID-19.

“Last night, over 1,000 people crowded on Ocean Beach to celebrate Burning Man,” Breed wrote Sunday morning. “This was absolutely reckless and selfish. You are not celebrating. You are putting people’s lives at risk. You are putting our progress at risk. No one is immune from spreading the virus.”

Breed wrote that talk of people returning on Sunday prompted the closure order and she said law enforcement will be patrolling the area.

“We know people love Burning Man and people want to get together this weekend,” she wrote. “But we all need to do our part. Stay home, stay safe.”

Elsewhere in the state, numerous parking lots to San Diego, Orange and Los Angeles County beaches closed after they filled to capacity and lifeguards reported seeing large crowds.

Campgrounds in the popular San Bernardino National Forest east of Los Angeles were also full, and rangers were out in force on “marshmallow patrols” — keeping an especially close watch for campfires and barbecues outside of designated sites that pose a potential risk of setting a wildfire. They also were worried that the surge of people could overwhelm mountain roads.

The heat wave was expected to spread triple-digit temperatures over much of California through Monday. Temperatures in downtown Los Angeles reached 111 degrees, while a record-shattering high of 121 was recorded in the Woodland Hills area of the San Fernando Valley. It was the highest temperature ever recorded in Los Angeles County, according to the National Weather Service.

The exceptionally high temperatures were driving the highest power use of the year and transmission losses due to wildfires have cut into supplies. Eric Schmitt of CAISO said up to 3 million customers could lose power for up to four hours Sunday evening.

The heat, coupled with a forecast of possible dry and gusty winds, made for dangerous weekend fire weather, at a time when nearly 13,000 firefighters already are battling to contain nearly two dozen major fires around California.

A wildfire that broke out near Shaver Lake in the Sierra National Forest has prompted evacuation orders Saturday as authorities urged people seeking relief from the heat wave to stay away from the popular lake. In San Bernardino County, a fast-moving fire in the foothills of Yucaipa forced the evacuation of Oak Glen, a farm community that just opened its apple-picking season this weekend.

In Napa County, officials on Sunday announced the lifting of all remaining evacuation warnings imposed during the Hennessey Fire, which Cal Fire reported was 91% contained as of 5:20 p.m.

Watch Now: Hennessey Fire as seen from Nichelini Family Winery in St. Helena

The Hennessy Fire as visible from property near Nichelini Family Winery.

With reports from Register reporter Howard Yune, Weekly Calistogan editor Cynthia Sweeney, Bay City News Service and The Associated Press.

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