Forty-two million people are under heat watches and warnings in the Southwest into the weekend as a heat dome strengthens over the region, with temperatures soaring to hazardous levels from Texas to Arizona and northwestward into California's Central Valley.
Why it matters: Extreme heat is the leading weather-related killer in the U.S., and the first such event of the season can be particularly dangerous since people are not yet accustomed to such high temperatures.
Threat level: Temperatures are forecast to climb into the 110s Fahrenheit in Phoenix through Sunday, with the National Weather Service warning of “very high heat risk” and cautioning the heat will be excessive “even by local standards.”
- Daily temperature records will be threatened in Las Vegas through the weekend.
- In Death Valley, California, the hottest place in the U.S., temperatures could reach or exceed 120°F for the first time this year, tying or breaking daily records there.
- The heat extends into California where triple-digit temperatures are forecast in Sacramento for the next three days. Outdoor labor will be especially dangerous, the NWS warns.
- Overnight low temperatures are forecast to remain elevated in Central and Southern California, likely breaking records Thursday and Friday nights.
- Overall in the U.S., overnight low temperatures have been increasing faster than daytime highs, and when the overnight temperature remains particularly warm it can be hard for the human body to cool down and get relief. This increases the risk of heat-related illnesses, which can be fatal.
- Urban residents and those without air conditioning are at the greatest risk.
Zoom in: In Phoenix, the heat is forecast to peak...