PHOENIX — Dangerous, record-busting heat spread across the U.S. Southwest on Tuesday and into parts of Utah, Montana and Wyoming as a dome of high pressure hovered over a large swath of the region, pushing temperatures into the triple digits this week and intensifying the risk for wildfires amid a long-running drought.
Some of the highest temperatures were seen in bone-dry Arizona, where the National Weather Service forecast a record high of 117 degrees (47 degrees Celsius) in Phoenix. The previous high for the date was 115 degrees (46 Celsius), set in 1974.
"It is kind of early to see temperatures this high, that's for sure," said Marvin Percha, senior forecaster at the weather service's Phoenix office.
Percha said the high pressure dome combined with the land's lack of moisture caused by extreme drought has combined to create blistering heat expected throughout the entire week.
"What is unusual is the strength and the duration" of the high pressure system, he said.
The temperatures in Phoenix also could break records the rest of the week, with highs expected to reach 116 Wednesday and 118 Thursday and Friday.
Stations where people can get water and cool off in the shade opened across the Phoenix metro area at Salvation Army posts, city swimming pools, libraries and community centers. They will operate during the day amid the excessive heat warning declared by the weather service.
People were warned to stay inside, drink plenty of water and not leave children or pets unattended in vehicles.
The excessive heat stretched from southeast California across Arizona and Nevada and into New Mexico, where a high of 103 degrees (39 Celsius) Monday at Albuquerque's airport set a record. It was expected to hit near that Tuesday.
Palmdale, in Southern California's Mojave Desert, hit 107 degrees (41.6 Celsius), breaking a record of 105 set in 1966.
"More records are at risk tomorrow," the National Weather Service for Los Angeles tweeted.
Salt Lake City set a heat record for the second day in a row, hitting 107 degrees Tuesday to tie its hottest temperature ever recorded, the weather service said. On Monday, Utah's capital reached 103 degrees to break a heat record for that date set nearly 50 years ago.
Some people cooled off at the Great Salt Lake outside Salt Lake City, floating in the water or playing along the shoreline.
Temperatures in the Las Vegas area also were rising toward possible records during what the weather service was calling the hottest spell in decades.
"It's just going up from here," said meteorologist Ashley Nickerson of the weather service's Las Vegas office.
The heat wave smashed daily temperature records in Montana and Wyoming and complicated the fight against several large wildfires. Strong winds with gusts up to 35 miles (56 kilometers) per hour were expected, threatening to stir up wildfires already burning and make it hard to stamp out new blazes.
A wildfire that broke out Monday near Yellowstone National Park in Montana grew quickly overnight and had burned more than 3 square miles (8 square kilometers) by Tuesday morning, according to the Custer Gallatin National Forest. Some people in the rural area were told to flee their homes, while other fires in the state also forced some evacuations.
Montana cities like Billings and Livingston and the Wyoming city of Sheridan at the base of the Bighorn Mountains set daily heat records, sometimes reaching as high as 108 degrees (42 Celsius).
"This is happening in the middle of June. This is unprecedented," said Bill Murrell, a weather service meteorologist in Riverton, Wyoming.
The heat wave hit at the start of the Southwest's annual monsoon season, which runs through Sept. 30 and is supposed to be the region's rainy period, often contributing as much as 60% of annual precipitation.
But last year's monsoon was the driest in recorded history, with an average of just 1.5 inches (4 centimeters) of rain in Arizona.
Percha, the forecaster in Phoenix, said June is Arizona's driest month and that the state doesn't usually start seeing some rain until early July.