'Extremely dangerous,' record-breaking heat wave takes hold across much of U.S.

An "extremely dangerous" heat wave is set to break daily temperature records across Western and Southern states through the holiday weekend, the National Weather Service warned Thursday.

The extreme heat comes as 28,000 people were forced to evacuate their homes because of a raging wildfire in Northern California. The Thompson Fire in Oroville, about 65 miles north of Sacramento, had grown to 3,568 acres and was only 7% contained Wednesday night.

California's Death Valley was 122 degrees. In the more populated parts of the Golden State, Sacramento sweltered at 99 degrees and Bakersfield was 108 Thursday afternoon, according to the National Weather Service. Downtown Los Angeles and San Francisco were a more mild 81 and 75 degrees, respectively.

The southern U.S. was covered by heat advisories or warnings Thursday. Birmingham, Alabama, was 94 degrees, but the heat index — a measure of how hot it feels that takes into account humidity — was 102 around 5 p.m.

Atlanta was 93; Shreveport, Louisiana 97; and Tulsa, Oklahoma was 98 degrees, with heat indexes making all those places feel like hotter than 100 degrees. The small Mississippi city of Greenwood was 97 degrees, but it felt like 114.

In total, more than 100 million people spent Thursday under heat alerts.

In the West, it will only get hotter and more dangerous.

The National Weather Service forecast temperatures of 110 to 115 degrees in inland California on Friday and Saturday. Parts of the desert Southwest could reach 120 degrees.

Afternoon temperatures could reach the upper 90s and the low 100s in the Northwest and parts of the Great Basin, the weather service said.

The weather service said the levels of heat across the Mojave Desert, the Sacramento Valley and the San Joaquin Valley "could pose a risk to anyone if proper heat safety is not followed."

Las Vegas is forecast to reach 117 degrees Sunday and 118 on Monday, each higher than the city's current all-time temperature record of 116.

The weather service advised people to stay hydrated and out of direct sunlight and in air-conditioned buildings where possible.

Records have already been broken: Livermore, on the eastern edge of California's Bay Area, reached 110 degrees, while San Rafael in Marin County, California, reached 100.

Parts of Arizona, Nevada and Texas just endured their hottest June on record.