PHOENIX (AP) — A blazing heat wave expected to send the mercury soaring to nearly 120 degrees (49 Celsius) in Phoenix and Las Vegas over the weekend settled across the West on Friday, threatening to ground airliners and raising fears that pets will get burned on the scalding pavement.

The heat was so punishing that rangers took up positions at trailheads at Lake Mead in Nevada to persuade people not to hike. Zookeepers in Phoenix hosed down the elephants and fed tigers frozen fish snacks. And tourists at California's Death Valley took photos of the harsh landscape and a thermometer that read 121.

The mercury there was expected to reach nearly 130 degrees (54 Celsius) through the weekend — just short of the 134-degree (57-Celsius) reading from a century ago that stands as the highest temperature ever recorded on Earth.

"You have to take a picture of something like this. Otherwise no one will believe you," said Laura McAlpine, visiting Death Valley from Scotland on Friday.

The heat is not expected to break until Monday or Tuesday.

The scorching weather presented problems for airlines because high temperatures can make it more difficult for planes to take off. Hot air reduces lift and also can diminish engine performance. Planes taking off in the heat may need longer runways or may have to shed weight by carrying less fuel or cargo.

Smaller jets and propeller planes are more likely to be affected than bigger airliners that are better equipped for extreme temperatures.

The National Weather Service said Phoenix reached 116 degrees (47 Celsius) on Friday, two degrees short of the expected high, in part because of a light layer of smoke from wildfires in neighboring New Mexico that shielded the blazing sun. Las Vegas still was expecting near record highs over the weekend approaching 116, while Phoenix was forecast to hit nearly 120 degrees (49 Celsius). The record in Phoenix is 122 degrees (50 Celsius).

Temperatures are also expected to soar across Utah and into Wyoming and Idaho, with triple-digit heat forecast for the Boise area. Cities in Washington state that are better known for cool, rainy weather should break the 90s next week.

The heat is the result of a high-pressure system brought on by a shift in the jet stream, the high-altitude air current that dictates weather patterns. The jet stream has been more erratic in the past few years.

Health officials warned people to be extremely careful when venturing outdoors. The risks include not only dehydration and heat stroke but burns from the concrete and asphalt. Dogs can suffer burns and blisters on their paws by walking on scorching pavement.

Cooling stations were set up to shelter the homeless as well as elderly people who can't afford to run their air conditioners. In Phoenix, Joe Arpaio, the famously hard-nosed sheriff who runs a tent jail, planned to distribute ice cream and cold towels to inmates this weekend.

Officials said personnel were added to the Border Patrol search-and-rescue unit because of the danger to people trying to slip across the Mexican border. At least seven people have been found dead in the last week in Arizona after falling victim to the brutal desert heat.

___

Carlson contributed in Death Valley, California. Also contributing were Robert Jablon in Los Angeles, Julie Jacobson and Michelle Rindels in Las Vegas, Michelle Price in Salt Lake City, Cristina Silva and Bob Christie in Phoenix and Susan Montoya Bryan in Albuquerque, New Mexico.