Russ Brown and other emergency officials in Yuba County have been trying to get the word out.

Charge your medical equipment and phone batteries now. Make sure you have enough nonperishable food to last a few days.

Because when the hot winds start blowing, the power to your house may be shut off.

The state is entering the height of fire season, with a dangerous mix of strong winds and temperatures approaching triple digits forecast across its valleys and foothills. For the first time this year, several Northern and Southern California communities simultaneously are facing preemptive blackouts to reduce the fire risks.

This is adding a new element of uncertainty and controversy in scores of communities.

“It’s the new normal we expect to see,” Brown said. “These shut-offs — they understand it, but it’s frustrating. It disrupts their lives.”

Pacific Gas & Electric has vowed to power down to avoid a repeat of last year’s Camp fire, in which thousands of homes were burned and 86 people were killed. Investigators identified downed PG&E equipment as the likely cause of the deadliest blaze in California history.

But the power shut-offs have generated debate, with some residents saying they create a whole new set of dangers as they try to watch out for news about fires. There has been heightened concern about those with health issues who rely on medical equipment to stay alive.

Some state and local officials have also complained that utilities don’t always give enough notice before turning off the power. And they have expressed concerns about communications and evacuations if the power is out, especially if traffic signals don’t work and cellphone service is affected.

Of the three big California utilities, PG&E was the last to adopt preemptive shut-offs as a strategy to reduce wildfire risks. San Diego Gas & Electric began doing them in 2013 and Southern California Edison in 2017. Each said it shuts off power only a few times a year and tries to limit the number of customers affected.

“What we’ve learned over the last two years is that the potential [for wildfire] is so great that we’re changing our practices,” said Robert Villegas, an Edison spokesman. “We’re monitoring year-round. There is no more seasons for us.”

On Sunday, Southern California Edison began notifying customers in Los Angeles, Santa Barbara, San Bernardino and Riverside counties that their power may be shut off starting Tuesday. About 45,000 customers — most of them in San Bernardino and Riverside counties — could be affected, Villegas said.

Thus far, San Diego Gas & Electric has not had to do any shut-offs this year. The company said it routinely monitors weekly forecasts and will begin notifications 48 hours ahead of any potential shut-off. It called a “public safety shut-off” a tool of last resort.

“Although we’ve made great efforts to protect our communities, there are still times during extreme weather when we may employ the use of Public Safety Power Shut-offs to try to prevent our electric system from becoming the source of an ignition which may endanger local residents and communities,” a company spokeswoman said in email.

Since Sunday, Yuba County has been telling residents on social media and its third-party alerting system, CodeRed, that they need to be prepared to go without power. About 5,300 residents were expected to have their power turned off at some point Monday evening, Brown said.

Over the weekend, the warnings to residents came in earnest in counties across Northern California: The days ahead were going to be hot and windy, and because of that you might have your power shut off.

At one point, it was estimated that some 3.8 million customers would have their power shut off by Pacific Gas & Electric out of concern that wind gusts could snap off a tree branch or damage a piece of equipment, creating a spark that could lead to the next wildfire disaster.

By Monday afternoon, those concerns were rapidly scaled back to three counties and thousands of customers in the Sierra foothills. PG&E decided not to proceed witrh evening shut-offs in Lake, Napa and Sonoma counties in the North Bay, and in El Dorado, Placer and Sutter counties in the Sierra foothills. The utility said it might shut off power to parts of those counties Tuesday, depending on the weather.

By Monday evening, the utility had began cutting power to 27,500 customers in Butte, Nevada and Yuba counties.

There’s not a single factor that will drive a public safety power shut-off event, but we definitely look at the humidity, the temperature and the wind speeds,” PG&E spokeswoman Megan McFarland said. She said the company began notifying customers in affected areas that shut-offs were possible. The notifications were made by robocalls, texts messages and emails starting at 8 p.m. Saturday, she said.

Brown said officials have been in constant communication with the utility and first responders about how to prepare.

Nearly all of California’s biggest and most deadly wildfires have occurred in the last 20 years, with many of them being sparked by equipment.

It’s that liability that pushed PG&E into bankruptcy earlier this year and has raised concerns that utilities may become more eager to shut off power to avoid potential catastrophe, even when the risks seem minimal.

“The seriousness we’ve seen has been with these extremely high-wind events, and now it’s moderate events,” Brown said. “I hope people don’t become numb to the messaging we put out.”

In the town of Paradise, news of the preemptive measure provided little comfort.

PG&E announced — then canceled — a power shut-off just before November’s Camp fire. Investigators with the California Department of Forestry and Fire Protection later determined the blaze was sparked by a transmission line, which PG&E said would not have been included in any preemptive shutoff.

“It’s frustrating,” Paradise City Councilwoman Melissa Schuster said Monday. “We heard this before the Camp fire. Power was not shut off. So rather than being relieved — and we’re coming up on Nov. 8 again — it’s a little bit of a trigger for most of us, I think. It’s where we were a year ago.”

The only big difference, she said, is that there’s not much left to burn.

She said that as residents rebuild, more are outfitting their homes with generators and solar panels to serve as backup power sources “because electricity is just not dependable anymore.”

“It’s kind of crazy,” she said. “It’s just one more thing that we all have to address in this ‘new now,’ being prepared for this type of thing.”

Meanwhile, a red flag warning is in effect from 1 p.m. Monday through 11 a.m. Wednesday in the Sacramneto Valley. Winds are estimated to be between 10 and 25 mph, with gusts between 30 and 40 mph, according to the National Weather Service. Slightly stronger winds are predicted in the Sierra foothills, with gusts up to 45 mph.

The western portion of the Sacramento Valley and neighboring foothills are facing the biggest fire threat because the highest wind gusts and lowest humidity are forecast there. The threat will be highest during the night and morning hours, when winds are strongest, the weather service said.

In the Bay Area, the red flag warning is in effect from 9 p.m. Monday through 5 a.m. Wednesday for the North Bay Mountains, East Bay Hills and the Diablo Range.

Strong winds are forecast for the higher elevations of Napa and Sonoma counties and the East Bay Hills, with gusts from 30 to 35 mph starting late Monday night. Wind gusts could reach 40 mph along some of the North Bay Mountains, where the fire threat will be most acute, forecasters said.

Cal Fire sent five engine strike teams and seven hand-crew strike teams to the northern part of the state, said Scott McLean, an agency spokesman. The teams arrived Sunday and Monday and included extra personnel.

The Los Angeles area will face brief but critical fire weather conditions Tuesday, as temperatures warm and Santa Ana winds develop, the weather service said.

Wind gusts could reach 25 to 40 mph in the mountains and valleys of Ventura and L.A. counties starting Monday night and persisting through Wednesday morning, with the strongest winds expected Tuesday morning.

Temperatures are expected to rise seven to 15 degrees Tuesday, with the biggest increase along the coasts and the coastal valleys, where highs are forecast in the 90s, according to the weather service. Some neighborhoods in the San Fernando Valley, including Woodland Hills and Van Nuys, are expected to see triple-digit temperatures.

The critical fire weather comes as the state is battling more than half a dozen blazes that are larger than 500 acres. Although California has already seen more than 157,000 acres burn in wildfires this year, that number is a fraction of how many acres had burned by this time last year, according to Cal Fire data.

Still, fire officials have cautioned this is the time of year when offshore weather patterns typically bring hotter, drier and windier conditions, drying out fuels and increasing the probability of ignition.

“September and October are historically the two months that we see the most significant wildfires, as far as most disastrous, largest and so on,” McLean said. “With the winds, fires take off very quickly, hence the red flag warning.”

Gov. Gavin Newsom sharply criticized President Trump in front of foreign leaders Monday, using his first appearance on the international environmental stage to highlight how California is addressing climate change, in contrast to the federal government.

“I don’t know what the hell happened to this country that we have a president that we do today on this issue,” Newsom said to applause at the opening ceremony for Climate Week in New York. “Because it’s a damn shame. It really is. I’m not a little embarrassed about it — I’m absolutely humiliated by what’s going on.”

Those who are attending the United Nations Climate Action Summit and surrounding events in New York City said the proceedings would give many international leaders their first exposure to Newsom while allowing the governor to signal where he plans to take California’s pioneering initiatives to address climate change. Other countries are watching closely to see how he carries a torch of activism lit by his predecessors.

“The new governor is not a known commodity,” said Robert C. Orr, special advisor on climate change to the U.N. secretary-general and dean of the University of Maryland School of Public Policy.

California is recognized as a world leader on climate policy, garnering continued interest from other nations for its work on emissions reduction, electric vehicles and renewable energy — an agenda that former Govs. Jerry Brown and Arnold Schwarzenegger championed.

Brown’s shadow, in particular, looms large. A longtime climate activist, Brown quickly embraced the role of being the American antidote to Trump when the president announced the nation would withdraw from the Paris climate agreement, a 2015 pact among nations worldwide to keep global warming below catastrophic levels.

On Monday, Brown launched the California-China Climate Institute at UC Berkeley, a partnership with China’s top climate change official, Xie Zhenhua, and the Institute of Climate Change and Sustainable Development at Tsinghua University.

Newsom praised the former governor in comments to fellow dignitaries and said he intends to continue the state’s tradition as a climate leader.

“I’m here [in] a long line of Democrats and Republicans in the United States that come from the state of California, that get it and want to get it done,” Newsom said. “I’m very proud to be a new governor, replacing now, following Gov. Jerry Brown, who demonstrably has been leading in international efforts.”

But to some, Newsom needs to do much more than Brown when it comes to fossil fuels.

Nearly two dozen protesters stood outside the Monday morning event and demanded the governor ban fracking and oil drilling in the state. Newsom said his legal advisors believe he cannot ban fracking solely through executive order and that the California Legislature would have to approve such an action.

“As Californians, in order for anybody, even Gov. Newsom, to claim he’s a climate hero he needs to start at the heart of it, which is stopping oil extraction,” said Jean Su with the Center for Biological Diversity.

Su held up one end of a California state flag decorated with hand-drawn oil wells, which she said she carried in similar protests against Brown during a U.N. conference on climate change in Bonn, Germany, in 2017.

Less than an hour after speaking at the Climate Week opening ceremony, Newsom addressed the annual meeting of the World Economic Forum, an international organization that seeks to build public-private partnerships to address global challenges. Then Newsom traveled to the U.N. headquarters, arriving shortly before Trump, and mingled with foreign dignitaries who had gathered there for the climate summit.

Thanks to Trump, the timing of the Newsom’s debut in New York couldn’t be better, said Ann Carlson, co-director of the Emmett Institute on Climate Change and the Environment at the UCLA School of Law.

The governor and the California Air Resources Board, in perhaps his administration’s most significant action to address climate change to date, struck a voluntary agreement with four automakers in late July to strengthen fuel efficiency standards. The deal would result in about one-third of new cars and SUVs sold in the U.S. to reach a minimum of 50 mpg by 2026.

Trump countered last week and said he would rescind California’s waiver to set its own rigorous vehicle emission standards, which gave Newsom a spotlight to push back on the president and take the fight to court.

“As a way to bolster Gavin Newsom as a climate leader, it’s hard to imagine a better opportunity for him than having the great climate denier in the White House going after him and the state of California,” Carlson said. “Newsom is standing up to that and it’s giving him a real opportunity to do so right before Climate Week.”

The governor’s international spotlight may overshadow the fact that he’s been “embroiled in a controversy” back home over his decision to veto the Legislature’s marquee environmental policy of the year, Carlson said.

Senate Bill 1, authored by California Senate President Pro Tem Toni Atkins (D-San Diego), would have allowed the state to keep Obama-era endangered species protections and water pumping restrictions for the Sacramento-San Joaquin River Delta. Newsom sided with water agencies that said the bill would have locked in outdated science on species protections and, as a result, threatened their water supply from the delta.

The governor sought to boost his environmental record ahead of the summit by signing an executive order that would encourage California’s public employee pension funds to focus on technologies and companies that mitigate climate change.

Newsom is scheduled to join governors from at least a half-dozen other states in the U.S. Climate Alliance at a news conference on Tuesday, before returning to the state on Wednesday.

“I want to take the baton and continue to move California’s leadership forward in the absence of national leadership on climate change and continue to express our desire to see more emulate the good work of California,” Newsom said.

One by one, each candidate who took the stage at an LGBTQ presidential candidate forum here got the same question and gave a nearly identical answer.

What would they do from Day 1 of their presidencies to address concerns of gay, lesbian and transgender communities, the moderators asked. Each of the first eight candidates responded with a list of positions that command widespread support among Democrats: lifting the Trump administration’s ban on transgender military service, backing passage of the Equality Act, appointing Justice Department officials committed to civil rights enforcement.

Then came Sen. Elizabeth Warren’s turn.

“I’m not going to tell you, I’m going to show you,” she said, as she pulled out a notecard and began to read: “Dana Martin, Jazzeline Ware, Ashanti Carmon …”

The auditorium fell silent as the litany of names continued. “… Bee Love Slater, Ja’Leyah-Jamar: Eighteen trans women of color who have been killed so far this year,” she said. “It is time for a president of the United States of America to say their names.”

The room broke into loud applause. Within moments, Warren’s hyper-efficient social media team had tweeted out the list to her followers. A short time later, when her time onstage ended after several more questions, the crowd — many of whom wore T-shirts and carried placards identifying themselves as supporters of Pete Buttigieg, the openly gay mayor of South Bend, Ind. — stood and cheered.

Afterward, it was clear the Massachusetts senator had added more converts to her growing list.

“Pete was fine,” one Buttigieg supporter was overheard saying to a friend. “But you can’t let yourself be out-energized by the grandma in the race.”

Warren has out-energized a lot of rivals over the last few months.

At a point when the still-large Democratic field has started to shrink, with candidates facing a third-quarter fundraising deadline that will probably drive more from the race, and when voter opinions have begun to gel, Warren has put herself in position to win this state’s caucuses and grab the mantle of front-runner.

The latest Des Moines Register poll, released Saturday night by J. Ann Selzer, the state’s most respected pollster, showed Warren in the lead for the first time, narrowly ahead of Joe Biden, 22% to 20%. Her rival on the left, Sen. Bernie Sanders of Vermont, who nearly won here in 2016, had slipped to third, at 11%, with Buttigieg and Sen. Kamala Harris of California trailing further behind at 9% and 6%, respectively. Sens. Amy Klobuchar of Minnesota and Cory Booker of New Jersey, both at 3%, were the only others with more than 2% backing.

More than four months remain before voters attend Iowa’s caucuses Feb. 3, the primary season’s first contest, and almost two-thirds of the likely voters in the poll said they could still change their minds. So Warren’s lead is hardly written in stone.

But the survey gave evidence her support could grow further: 71% said they were at least considering Warren, significantly more than the 60% for Biden and more than any other candidate.

As Friday night’s forum showed, Warren has attracted support by combining two skills often not found together — careful preparation and attention to details on the one hand, and, on the other, an ability to connect emotionally with her audience.

In her rallies, Warren taps into much of the same voter anger toward government and the political system that President Trump feeds on, while offering a dramatically different solution.

Where Trump plays off his supporters’ resentment of “the elites,” Warren denounces the corrupting power of money. She has honed her case into a succinct argument that she laid out this way at an event Thursday evening in Iowa City:

“Whatever issue brought you here tonight, whether it’s gun violence, healthcare, education — whatever brought you here — there’s a decision to be made in Washington: I guarantee, it’s been influenced by money.

“When government works for the wealthy and the well connected, when government works for those who have money, when government works for those who hire armies of lobbyists and lawyers and is not working well for everyone else, that is corruption pure and simple, and we need to call it out for what it is.”

She studiously avoids mentioning her rivals by name but offers an unmistakable contrast with Biden when she declares that “we’re not at a moment where you can say, ‘I know, I’ve got two statutes over here and one regulatory change over there, and we’ll change the head of a department over there.’ No, we need big, structural change in this country.

“How do we get there? I’ve got a plan.”

Biden more directly, although politely, criticizes “my friend Elizabeth” — most specifically over her support for “Medicare for all,” which he attacks as a politically unfeasible project that would require a huge, unsustainable tax increase that Warren, unlike Sanders, has never acknowledged.

“You can’t beat Trump by not being straightforward,” Biden said Friday at a town hall event in Cedar Rapids when he was confronted by a voter who supports Medicare for all. “Tell Elizabeth to tell it’s going to cost a lot of money, and she’s going to raise people’s taxes doing it.”

More broadly, he defends an approach to government that his critics consider overly cautious and incremental.

“You can’t leave out entire segments of society and expect to get things done; you’ve got to know how to negotiate, you’ve got to know how to bring people together, generate consensus,” he said in answer to a question about climate change and the disastrous floods that have hit the Midwest in recent years. “That’s something I’ve spent my whole life doing.

“And I know everybody says, ‘Well, you know you can’t cooperate anymore,’ but if you can’t cooperate anymore, get ready, get your flippers out and your wetsuit.”

That call for compromise appeals to many of Biden’s supporters.

“He knows how the system is supposed to work — and that’s very important right now,” said Dow Bates, 84, a chiropractic physician from Des Moines, as he waited with his wife for the speakers at a multi-candidate event known as the Steak Fry.

Bates, recalling how the tea party movement dragged Republicans, including Iowa Sen. Charles E. Grassley, to the right, said he feared a similar dynamic could make the Democrats more radical.

“We need a viable democracy where we can work things out. And we’ve lost that,” he said. “We don’t have a real Republican Party now. I hope that a similar schism on the left doesn’t make it so the Democrats can’t get anything done even on their side.”

Along with their contrasting views, the two candidates offer a sharply divergent subtext to which voters respond: People go to Warren rallies seeking excitement; they attend Biden events for reassurance.

“We’d like someone moderate,” said Dave Nelson, 76, a resident of Hiawatha, a suburb of Cedar Rapids. He was one of about 200 voters, mostly middle-aged and older, at Biden’s event.

“We have to make sure we don’t have an extreme liberal as our candidate; that just gives people an excuse to vote for Trump,” he said as he and his wife, Orla, waited for Biden to speak.

The two admire Biden, said Orla, 75. “He’s got a lot of wisdom.” But they worry about him, too, and hope he picks a strong running mate if he becomes the nominee.

“We need someone like Amy [Klobuchar] in there to back Biden up if his energy fails him,” she said. “He’s got to be really careful about who he chooses.”

Although Warren, who turned 70 in June, is only 6 ½ years younger than Biden, who will turn 77 in November, voters don’t seem to view the two as similar in age. Her rallies, from the jogging onstage thatinvariably opens them through the lengthy selfie line that ends them, convey a message of vigor.

The crowd at her Thursday evening event was about 10 times larger than Biden’s, and about900 stayed for as long as an hour and a half afterward to get selfies with the candidate.

Susan Futrell and Flora Cassiliano, neighbors in Iowa City, were near the end of the line. Both said they were still weighing several candidates but praised Warren’s energy and stamina.

Biden and Sanders “are tremendous public servants,” said Futrell, who noted thather first Iowa caucus was for George McGovern in 1972 when she had just turned 18.

“I like to respect them for that,” she said, but “I don’t believe that an old, white guy is the only safe choice. Why would we look backward?”

She had hesitated about Warren because “I worried about her being a heady professor, a policy wonk,” she added. “Instead, what I see is she’s really able to tell her story.”

Times staff writer Melanie Mason in Des Moines contributed to this report.