Millions of blasting air conditioners strained electric grids, prompting Texas and California utilities to threaten shut-offs. The National Weather Service in Las Vegas tweeted all-caps appeals for residents to stay hydrated and stay inside: “Long duration heat waves are DEADLY.” Doctors from Palm Springs to Phoenix warned about pavement so scorching it can give people third-degree burns.

Fueled by climate change, the first major heat wave of the summer has seized the western United States, toppling records and threatening lives. The event is unprecedented in its timing, intensity and scope, said Washington State University climate scientist Deepti Singh; never have such severe conditions been recorded over such a large area so early in the summer.

At least five weather stations, including Salt Lake City and Palm Springs, Calif., have matched their all-time high temperatures this week, months before the hottest part of the season. Las Vegas set a new daily record, at 116 degrees. In Death Valley, Calif., on Thursday, thermometers read 128 degrees.

Coupled with a catastrophic drought that has damaged crops and shrunk vital reservoirs to all-time lows, the blazing weather is a trademark of human-caused warming, Singh said.

California's extreme drought has forced farm manager Salvador Parra to fallow 2,000 of his acres and dig deep for water to save the crops already planted. (Reuters)

Unless the world drastically cuts greenhouse gas emissions, summer temperatures in the West could rise by as much as 6 degrees Fahrenheit by the middle of the century. The number of extremely hot days in the United States could triple, and the duration and extent of heat waves would become more extreme.

In the meantime, more than 40 million residents of Western states must endure a bout of broiling conditions that shows no sign of letting up. Temperatures are forecast to hit 115 degrees and higher this weekend in cities spanning the Southwest. Red-flag warnings are in place across New Mexico, Utah, Arizona and Colorado as dry lightning and gusty winds threaten to spark new wildfires.

People sought relief wherever they could find it: in the shade of trees, the spray of playground sprinklers, the air-conditioned lobbies of government buildings.

“At Circle Ks, they give you free ice,” said Bruce Simmons, 58, who has been sheltering in Phoenix’s Cortez Park, along with his wife and three children, since the family was evicted.

“You look for the 24-hour QTs, where they have safe havens. They’ll let you hang out,” he continued. “There are a few 24-hour Denny’s where as long as you buy a soda, they’ll let you sit in there for a while and then you can sleep in their parking lot. You try not to hit the same place twice in a row.”

It was 117 degrees in Phoenix on Thursday afternoon, breaking the city’s previous daily record by three degrees.

“You learn ways to stay out of the heat after awhile,” Simmons said. “You have to.”

At Sacramento County’s Department of Human Assistance on Thursday, 54-year-old Suzy Fobbins sat on a plastic chair beside everything she owned: a cart with clothes, a rolled-up tent, a sleeping bag and a cellphone.

Normally, Fobbins said, she lives in a parking lot in a different part of town. But she almost passed out inside her small tent when the temperature began inching up to 100 degrees earlier this week.

“I started retching,” she recalled. “I couldn’t see, I was so dizzy.”

Fobbins has asthma and diabetes, and she knew she wouldn’t be able to withstand Thursday’s forecast of 109 degrees. So when a probation officer mentioned this refuge, she got on the bus.

She hoped she would be able to get a motel room through a service operated by the Federal Emergency Management Agency. Otherwise, she would have nowhere to go after 8 p.m., when the office building closed and the mercury would still be hovering around 100.

“You can’t live like that,” Fobbins said. “A lot of people are going to die in this heat, because they don’t know where to go.”

Sweltering nights are a trademark of climate change, which is increasing overnight lows at nearly twice the rate of daytime highs.

“It can be miserable,” said Anna Bettis, who manages the Nature Conservancy’s healthy cities program and lives in south Phoenix.

For the past two nights, temperatures in the city haven’t dropped below 90 degrees. By morning, the sun feels like an assault.

“It’s kind of like your skin is almost sizzling,” Bettis said.

She worries about the toll of heat on the city’s most vulnerable residents. Experts consider extreme heat to be the deadliest kind of weather disaster. Without water, shade and a chance to cool off, the body’s ability to regulate temperature becomes overwhelmed — a condition known as heat stroke. Cells start to break and internal organs shut down. The threat is especially severe for people who are elderly, homeless or suffer from preexisting health problems, such as cardiovascular disease and diabetes.

Maricopa County in Arizona — one of few places to consistently track the health effects of heat — attributed more than 300 deaths to extreme temperatures last year. Since April, the county has recorded three heat-related deaths and is investigating 20 more.

A network of government agencies and community groups in the region has scrambled to turn shelters and offices into emergency cooling centers. At the nonprofit St. Vincent de Paul campus in south Phoenix, some 200 cots now fill what used to be a dining hall. Coolers by the entrance are stocked with water, popsicles and ice.

Associate CEO Shannon Clancy watched a steady flow of overheated men and women shuffle tiredly into the building.

“The last few mornings, we’ve seen a warm sea of people who are out in the elements all day and then really can’t cool off at night either,” she said. “It’s crucial be able to really give people that respite, where their core body temperature can come down, where they can get water and get hydrated again.”

In California’s Central Valley, volunteers with Líderes Campesinas — a network of female farmworkers — drove from field to field, distributing water and warning workers about the dangers of heat. Their advice: take breaks, seek shade, watch for signs of stroke.

“It takes a huge toll on the body to be out there,” said Irene de Barraicua, a spokeswoman for the group.

According to the Centers for Disease Control and Prevention, farmworkers die of heat at roughly 20 times the national rate. But there is no national temperature standard for outdoor laborers; California is one of only a few states where farms are required to provide access to water and shade.

Even businesses devoted to cooling people off were struggling. At Cowabunga Bay Water Park in Henderson, Nev., owner Shane Huish concluded there must be an upper temperature limit on people’s enjoyment of waterslides.

“When it gets this hot, 115 to 116 degrees, our numbers sort of level off,” he said. “Sometimes, it just gets too hot for people to be out. We’re competing with air-conditioned homes.”

Most of the roughly 5,000 people who did come to the park spent their time in the lazy river and wading pools. It wasn’t worth waiting in line for rides in the heat.

This heat wave is made worse by the desperately dry conditions in the region. More than half of the western United States is currently experiencing “extreme” or “exceptional” drought, indicating widespread water shortages and major impacts on crops and pasture. Critical snow packs in the mountains of Utah and Colorado were 30 to 50 percent below normal and melting fast. Water levels at major reservoirs have hit all-time lows. The federal government has cut water allocations to some California municipalities by 75 percent, while farmers across the Southwest contemplate crop failures.

The persistent lack of moisture amplifies already scorching conditions, scientists say. The energy required to turn water into vapor usually brings down temperatures — that’s why evaporating sweat helps cool a person off.

“But right now, because of how dry it is, all that energy is just going into heating our atmosphere and heating the surface,” Singh said.

In turn, the heat wave is certain to exacerbate existing water issues. Hot air holds more moisture, sucking every drop of liquid from plants and soils. This, in turn, will set the stage for catastrophic wildfire and heighten the severity of blazes already underway.

In Arizona, the heat has made it unsafe for some firefighting aircraft to fly, the state’s top fire official told legislators this week. Meanwhile, the scarcity of water means pilots are struggling to find places where they can scoop up water to drop on the more than a dozen fires already burning across the state.

The combined heat and drought are also drying out vegetation and turning vast swaths of forest into potential wildfire fuel.

“Everything points to it being even worse than last year,” said Singh, who spent weeks sheltering from wildfire smoke that engulfed the region last September. “It’s terrifying.”

Mark Kreidler in Sacramento, Ryan Slattery in Las Vegas and Jimmy Magahern in Phoenix contributed to this report.