Temperatures are expected to reach potentially lethal levels this weekend in parts of the Southwest and the Plains. Forecasters say major cities including Phoenix, Las Vegas and Tucson, as well as parts of Kansas and Oklahoma, will reach highs above 110 degrees Fahrenheit.

The National Weather Service has issued widespread excessive heat warnings, and says such high temperatures are "rare, dangerous, and deadly." The agency is urging people in the affected areas to cancel outdoor activities between Saturday and Tuesday. The heat wave is expected to peak Sunday.

In Phoenix, where temperatures are expected to be highest, the heat wave could break records. The highest temperature ever recorded there, in June 1990, is 122 degrees, and the National Weather Service says this weekend's system could rival that heat wave.

Local emergency managers and state departments of health in more than a dozen states are warning people to seek out air-conditioned spaces, drink more water than usual, and check on elderly people and people who are living alone.

According to the Centers for Disease Control and Prevention, about 500 people die of heat-related causes each year in the U.S.

The hot, dry weather is also making wildfires in the western U.S. more severe. In Southern California, where temperatures are expected to be in the low triple digits, hundreds of firefighters are battling a 1,400-acre fire burning near the coastal city of Santa Barbara. In New Mexico, hot, windy weather is already feeding a fire in the central part of the state and state authorities have issued mandatory evacuation orders.

Fire crews in Arizona are struggling to control the Cedar Creek blaze, which has thousands of Arizona residents living under pre-evacuation advisories going into the weekend. Navajo County Sheriff KC Clark says he hopes they are "out of the woods" before the extreme temperatures hit Saturday and Sunday.

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