PHOENIX — A blazing heat wave expected to send the mercury soaring to nearly 120 degrees in Phoenix and Las Vegas settled over the West on Friday, threatening to ground airliners and raising fears that people and pets will get burned on the scalding pavement.
The heat was so punishing that rangers took up positions at Lake Mead in Nevada to persuade people not to hike. And tourists at California’s Death Valley took photos of a thermometer that read 121.
The mercury there was expected to reach nearly 130 Friday — just short of the 134-degree reading from a century ago that stands as the highest temperature recorded on Earth.
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 hurts engine performance. Planes taking off in the heat may need longer runways or may have to shed weight by carrying less fuel.
The National Weather Service said Phoenix could reach 118 Friday. Las Vegas could see the same temperature during the weekend in what would be a record for Sin City. The record in Phoenix is 122.
Temperatures are also expected to soar across Utah, 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.
‘‘This is the hottest time of the year, but the temperatures that we’ll be looking at for Friday through Sunday, they’ll be toward the top,’’ said National Weather Service meteorologist Mark O’Malley.
‘‘It’s going to be baking hot across much of the entire West.’’