A rare heat wave event is forecast this weekend, says the National Weather Service.

Parts of the southwestern United States are under an excessive heat warning this weekend. Temperatures are forecast to reach 120 degrees Fahrenheit in some areas, and authorities urge people to take precautions as such high heat can become deadly.

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The National Weather Service forecast predicts a maximum of 126 in Death Valley, California. Phoenix, Arizona, expects a peak of 117 on Sunday, and Las Vegas, Nevada is gearing up for the weekend highs of 113.

The National Weather Service uses different criteria for heat warnings in different parts of the country. An excessive heat warning indicates unusually high temperatures that could present considerable health risks.

In the southwest, “we use what we call a heat hazard,” said Marvin Percha, a meteorologist with the National Weather Service. This is different from other areas of the country where heat rates are more important in heat warnings.

“We look at how rare the event is and compare what is normal,” said Percha. “Given the temperatures we have forecast now, we are facing a rather rare event.”

The heat in Phoenix this weekend could break daily records. Phoenix’s expected high of 117 on Sunday would break the daily record of July 12, 115, set in 2009. The heat in California and Nevada will be close to, but not quite reaching, the records.

High heat is seasonally appropriate for the region, but is generally not as high for that long.

Friday marks the 107th anniversary of the hottest day on earth ever recorded, when Death Valley reached 134 degrees Fahrenheit, CNN meteorologist Pedram Javaheri said.

Such high temperatures can be amplified in valleys and on the ground, where materials can begin to melt.

While monthly records may not break this weekend, the excessive heat is part of a general trend of rising temperatures. High temperature patterns are just one of many extreme weather events exacerbated by climate change.

High temperatures can be dangerous and people in affected areas are urged to take safety precautions. “Anyone with diabetic or heart problems should be especially careful about this and really do everything they can to prevent it,” Percha said.

According to the Centers for Disease Control, heat-related illness kills more than 600 people per year. Stay safe by staying indoors, staying hydrated, wearing light clothing, and knowing the symptoms of heat illness.

“If you have to be outside, try to limit your exposure and stay well hydrated,” Percha said. “Find air-conditioned cooling centers if necessary.”

Phoenix has a map of public cooling centers. Check with local officials to find your nearest cooling center or water donation location.

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