More than 70 million are under heat warnings and advisories this weekend through early next week as a potent heat dome sends temperatures soaring to levels the National Weather Service is calling "potentially deadly."

The big picture: The heat wave, made worse by a long-term, climate change-influenced drought, shows signs of eventually swelling into the middle of the country and then eastward through next week.

Why it matters: Extreme heat is the deadliest weather-related hazard in the U.S. each year, and climate change is making these events more likely, severe and long-lasting.

• The public health threat of this particular heat wave is especially elevated because of the high overnight minimum temperatures, which in many locations are breaking records. For example, at 1 a.m. local time Saturday morning, Phoenix was still at 100°F.
• "Extreme and deadly heat will continue through this weekend," the NWS forecast office in Phoenix stated, noting the "minimal overnight recovery." Forecasters noted that Phoenix may see its earliest-ever 90°F overnight low temperature.

Of note: The city has opened numerous cooling centers for those without access to air conditioning.

By the numbers: Heat advisories blanket nearly the entire state of Texas and Oklahoma, and extend as far east as Tennessee.

• These advisories and a more serious warning, known as an excessive heat warning, also are in place all the way to the West Coast, with triple-digit heat roasting California's Central Valley.
• Daily temperature records already have been set beginning Friday, and more are likely to fall Saturday and beyond. Overall, temperature departures from average during this heat wave are about 10 to 20°F or more above normal for this time of year.

Friday's record highs included:

• 109°F: Las Vegas.
• 123°F: Death Valley, Calif., where the hottest temperature in the world was recorded. This was one of the earliest 123-degree readings ever recorded in the U.S., tweeted weather historian Maximiliano Herrera.
• 113°F: Phoenix.
• 103°F: Austin.
• 100°F: Albuquerque
• 98°F: Houston

What's next: High temperatures in the Southwest are likely to peak Saturday and Sunday, before the core of the high-pressure area, or heat dome, shifts eastward and parks itself over the Tennessee River Valley.

• The clockwise air circulation around this high will pump hot and humid air northward. The National Weather Service is forecasting high temperatures on Tuesday into the upper 90s as far north as Chicago and Minneapolis, with triple-digit heat potentially reaching Iowa.
• Computer model projections show that the heat may not relent for parts of the Central U.S., South and Southeast until next week, before the heat potentially slides back to the West.

Context: More frequent and severe heat waves are one of the clearest manifestations of human-caused global warming, studies show.

• In multiple instances, including last year's deadly Pacific Northwest heat wave, researchers have found that extreme heat events are occurring today that would be virtually impossible without human-caused global warming.

Go deeper: Heat waves could soon have names