PHOENIX — In 50 degree temperatures, some airplanes might not take off. Power grids strain as the outside air keeps transmission lines from cooling. And for desert dwellers, a cold bottle of water and some shade can mean the difference between life and death.

In Phoenix, the high for Saturday was 44. But meteorologists believe the next two days could be record-breaking. Officials are warning residents the mercury may rise to 49 on Sunday and Monday, approaching the city’s record of 50.

Airlines will be monitoring temperatures as excessive heat can throw off performance calculations preventing planes from taking off, said Polly Tracey, spokeswoman for American Airlines.

Tracey said they may have to have to delay flights until the heat lets up, but officials will have to wait and see before making any decisions.

The Phoenix parks department is posting extra rangers at hiking trails warning visitors of the dangers and asking them to be off the trails by noon.

Arizona’s power companies are prepping extra maintenance crews and securing extra power to keep the cool air blowing, said Jacob Tetlow, general manager of operations with Arizona Public Service Co.

Excessive heat contributed to 84 deaths in the state last year, officials said in Maricopa County, the state’s largest. Officials already confirmed this year’s first heat-related death – an elderly woman who died from heat exposure in her backyard in early June.

Dr. Cara Christ, director of the Arizona Department of Health Services, is warning residents to watch for signs of heat illness: thirst, red skin, cramping, exhaustion and a lack of sweat. The agency is telling local officials to prepare for an influx of heat-related illnesses.

Arizona’s hottest day on record was in 1990 when temperatures hit 50, said Nancy Selover, state climatologist. Airlines grounded all the flights out of Phoenix Sky Harbor International Airport, she said.