An elderly man was found dead on Saturday in a home without air-conditioning in Las Vegas, where the city's temperature reached 115 degrees, tying the record for the hottest June 29 since 1994. Also, more than 200 people attending an outdoor concert there were treated for heat-related problems that day, 34 of them at hospitals, the authorities said.
At trailheads at the Lake Mead National Recreation Area in Nevada, park rangers were trying to dissuade people from hiking the same area where a Boy Scout troop leader died of heat exposure early last month, when temperatures were lower.
At Death Valley National Park in California, whose temperature of 134 degrees a century ago stands as the highest ever recorded in the world, the digital thermometer became a busy tourist attraction over the weekend. The forecast called for a high of around 130 degrees at the park's Furnace Creek area on Sunday; leaflets at the visitor center warned "Heat Kills."
Because summer brings the highest rate of deaths among migrants trying to enter the United States illegally through Arizona, the Border Patrol added extra members to its elite search and rescue team. At least seven migrants had been found dead in the desert over the past week.
Monsoons normally bring rain and cooler temperatures to the region in July, but the heat has shown no sign of abating. Several Western states were under heat warnings on Sunday, with most of those expected to remain in effect at least through Tuesday evening. Meteorologists warned of the potential for forest fires in drought-plagued communities in Arizona, California, Colorado and New Mexico, as the clouds that build early in the monsoon season often bring lightning and wind but little or no rain.
In Arizona, a fire sparked by lightning near Prescott on Friday forced the evacuation of several subdivisions on Sunday afternoon as it continued to grow. Lightning had already started four forest fires outside New Mexico's capital, Santa Fe, on Friday. On Sunday, one of them was still burning.
"We're really kind of on the edge of our seats now and over the next week or two," said Todd Shoemake, a meteorologist with the National Weather Service in Albuquerque.
On Saturday, as the temperature reached 119 degrees in Phoenix, making it the city's fourth hottest day on record, US Airways canceled 18 of its regional flights because the maker of the smaller jets that fly those routes had provided performance statistics only up to temperatures of 118 degrees.
Todd Lehmacher, a spokesman for the airline, said there was no way to know for sure, for example, how long a runway the planes would need to safely take off. (For larger aircraft, the information covers temperatures up to 126 degrees, Mr. Lehmacher said. The highest temperature on record in Phoenix is 122 degrees.)
It has been so hot here in Phoenix that tigers at the zoo were served frozen fish treats and elephants were doused with hoses to keep them from overheating. Butterflies were found collapsed on the pavement, felled, apparently, by the scorching temperatures. Mesquite trees, staples of the desert, closed their tiny leaves to protect themselves from the heat.
"This is payback time for those days that we're happy not to be the ones shoveling snow out there," Marcus Morrison, 34, said as he stood at a bus stop here on Sunday, a wet towel draped around his neck.
A wispy layer of clouds moved over the city on Friday, trapping the heat like a lid on a pot of boiling water. Temperatures here had not dipped under 90 degrees since Thursday morning, and there was no sign of immediate relief in the forecast for Phoenix and elsewhere in the region. Forecasters say part of the problem is that ocean breezes have not been traveling far enough inland to cool the desert.
Ken Waters, a warning-coordination meteorologist for the National Weather Service in Phoenix, said a strong high pressure system had been parked over much of the West for days. It is forecast to weaken during the week, but, he cautioned, "I'd be foolish to call it a cooling trend."
It is only on Friday that the daytime temperatures here and in several other cities, like Palm Springs, Calif., and Las Vegas, are expected to drop below 110 degrees. Overnight temperatures are also expected to remain high — above 90 degrees in some cities and, in others, almost there.
The heat did not stop tourists from going outside on the Las Vegas Strip, which was thick with pedestrians sweating through tank tops over the weekend. On Saturday, Deanna Harney, who had traveled from Boston to celebrate her sister's 50th birthday, threw her arms up to celebrate the hot weather, saying: "I love it! It's been raining back home."
Nearby, Joe Mendoza suffered under a Mario Brothers costume as he posed for pictures with tourists in exchange for tips.
"I brought frozen water bottles, and I drink at least one every hour," Mr. Mendoza said through a large foam head.
Most of the people he sees, he said, "don't look like they're having a lot of fun either."
Heath Haussamen contributed reporting from Las Cruces, N.M., and Lynnette Curtis from Las Vegas.
