Excessive Heat Warnings Issued in Northwest, 13 Million Face 'Dangerous' Temperatures

Excessive heat warnings have been issued for nearly all of Washington and Oregon, most of Idaho and parts of northern California.

The National Weather Service has warned that a "dangerous heat wave," bringing record-breaking, triple-digit temperatures, is expected this weekend and next week across the northwestern U.S.

More than 13 million people are under an excessive heat warning or watch as the "prolonged heat wave" begins, the NWS tweeted on Thursday.

An excessive heat warning is issued when "the maximum heat index temperature is expected to be 105 [Fahrenheit] or higher for at least 2 days and night time air temperatures will not drop below 75," according to the weather service.

It adds: "However, these criteria vary across the country, especially for areas not used to extreme heat conditions. If you don't take precautions immediately when conditions are extreme, you may become seriously ill or even die."

Friday is expected to be "the first of many extremely hot days" across the northwest. Temperatures are predicted to reach "well into record-breaking territory" from Saturday through at least the middle of next week, the NWS said.

In Washington and Oregon, temperatures are forecast to hit 20 to 30 degrees above average this weekend, with "widespread temperatures in the upper-90s and triple digits" in Portland and Seattle.

The NWS added that temperatures across the Columbia Basin in western Washington and north-central Oregon could reach 110 F.

An extreme heat watch—which is issued when "conditions are favorable for an excessive heat event in the next 24 to 72 hours"—is in effect in parts of southern California, including Los Angeles and San Diego, as well as western Nevada and southeastern Idaho, the NWS said.

San Diegans could see mercury levels rise to 110 F in the desert areas, while "elevated fire weather conditions" are expected in the inland valleys, mountains and deserts of the Los Angeles area from Saturday to Wednesday

An excessive heat watch is in place for Sunday afternoon through Wednesday evening in parts of Nevada and California.

The NWS has warned that "dangerously hot conditions," with temperatures up to 105 F, are possible for northeast California, the Sierra Front and Mineral County. Mercury levels could reach 108 F in the Basin and Range region of western Nevada, including Fallon and Lovelock.

The federal agency warned: "Heat of this magnitude can be extremely dangerous if proper precautions aren't taken. Residents are urged to stay hydrated, avoid extended amounts of time outdoors and stay in air-conditioned rooms.

"Night time temperatures are only expected to briefly cool into the 70s throughout the lower elevations, which can significantly increase the threat for heat related illnesses."