A punishing heat dome is building across as much as two-thirds of the continental United States, with roughly 44 million Americans under heat alerts as temperatures are forecast to soar past 43°C across the Rocky Mountains and northern Plains this weekend. The National Weather Service predicts more than 90 local records will be tied or broken through Wednesday, and forecasters expect record triple-digit highs in Nevada, Utah, Colorado, Wyoming, Idaho, Montana, North Dakota and South Dakota. Las Vegas is projected to reach 111°F on Saturday, while Salt Lake City faces unprecedented heat.
The danger extends overnight, with temperatures holding above 80°F after dark in several Gulf and Atlantic coastal cities. In Washington, Oregon, Idaho, Montana and Wyoming, wildfire risk is heightened.
The wave follows a bout of extreme heat in the East last week and arrives as El Niño has an 81% chance of becoming very strong by autumn.