Afternoon temperatures in the Arizona state capital, Phoenix, are expected to reach 120F (49C) in what local media has called a “hellscape” heatwave.

At the city’s Sky Harbor airport, one of the 10 busiest in the US, dozens of flights have been cancelled because of the predicted heat. High temperatures make the air thinner, reducing lift and impairing an aircraft’s performance.

Many American Airlines’ regional services use Canadian-build Bombardier CRJ aircraft, which are not certified to operate above 118F (48C). So the airline has pre-emptively cancelled around 50 flights that were due to be operated by Skywest and Compass airlines under the American Eagle brand.

Most of the affected flights are to and from Phoenix. But anyone hoping to leave their home in Tucson, Arizona, for some California grass will find that flight AA6031 to Los Angeles has also been cancelled.

Some services to and from Flagstaff/Grand Canyon are also grounded; the airport is at an altitude of 7,000 feet. “Hot and high” airports are especially challenging because of the rarefied air.

The US National Weather Service has told tourists visiting the Grand Canyon that temperatures at the Colorado River base could reach 116F (47C). A bulletin in effect until Friday evening warns: “Temperatures are expected to rise to dangerous levels.” Day hikers on Bright Angel Trail have been warned not to descend no further than 1.5 miles, and told to wear a wide-brimmed hat and sunscreen. They are also urged to take salty snacks as well as sufficient water and an electrolyte mix.

Airbus and Boeing jets are able to operate at higher temperatures, but performance may still be impaired by heat. Earlier this month Hainan Airlines decided to delay the departure of its flight from Las Vegas to Beijing for the summer, because of the capacity restrictions imposed by high afternoon temperatures.