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American Eagle planes sit on the tarmac at Ronald Reagan Washington National Airport in Arlington, Virginia, Jan. 24, 2017. Getty Images

A bout of extreme heat in Arizona led to the cancelation of almost 50 flights out of Phoenix’s Sky Harbor International Airport Tuesday. As temperatures were expected to reach up to 120 degrees Fahrenheit in the afternoon, American Airlines grounded many of its American Eagle regional flights departing between 3 p.m. and 6 p.m.

American Eagle flights, which operate using smaller Bombardier CRJ aircraft, are constructed to withstand temperatures of up to 118 degrees.

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“Our smaller regional operations – those that use our CRJ aircraft types – will be most affected by the heat,” airline communications specialist Kent Powell told CNN Tuesday. “We really aren’t expecting any change to the operation with our mainline aircraft.”

Larger jets, like Boeings and Airbuses, are able to withstand temperatures of about 127 degrees, allowing them to operate in extreme temperatures like those in Phoenix Tuesday. But smaller planes are affected by heat during takeoff. As temperatures increase, a plane needs more speed to lift off and certain runways might not be long enough to allow for such speed to be reached, according to the Arizona Republic.

More flight cancelations could come as Tuesday progresses and temperatures climb further, an airline spokesperson told CNN.

Temperatures reached 118 degrees Fahrenheit Monday in Phoenix, tying the region's record set June 16 last year. And temperatures remained high even as night fell: at 9:30 p.m. Monday, temperatures were still topping 109 degrees Fahrenheit. And heat is affecting more than just Arizona—more than 29 million residents in California were under a heat warning or advisory Tuesday and excessive heat warnings were issued in southern Nevada, California, and Southwest Arizona until Friday. The National Weather Service forecasted a high of 127 degrees Fahrenheit in Death Valley, California, calling the heat wave, “extreme even by desert standards.”

Power outages and wildfires have also been reported as a result of the excessive heat. Certain lanes of a freeway in West Sacramento buckled under the temperatures, a television station in Phoenix aired a live stream of a 600-pound block of ice and a team of meteorologists in Sacramento baked cookies and fried bacon inside a vehicle.

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Authorities warned about the dangers of heat illness and urged people to be vigilant about not leaving pets or children inside a car for any time at all. United States Border Patrol, in addition, ramped up its warnings for those attempting to cross into the country by way of the Sonoran Desert and said it had its search and rescue team on high alert.

“It is physically impossible for the average person to carry enough water to survive several days of walking through the desert,” Border Patrol said in a statement Tuesday.