A record-challenging heat dome is about to bake the West with the summer’s hottest temperatures so far

By Meteorologist Tyler Ory and Andrew Freedman, CNN

(CNN) — An unusually strong heat dome will scorch much of the western United States this weekend, bringing the hottest temperatures so far this year to tens of millions from California to Canada.

Dozens of record highs are expected to fall in at least 12 states in the West through the weekend with around 40 million people under heat alerts. Over 10% of the continental US will experience their hottest day of 2026 to date in the coming days.

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High temperatures will climb to more than 10 degrees above normal — even for the peak of summer — from Southern California through Wyoming and Colorado from Friday through Tuesday. Death Valley, California, is forecast to reach a blistering 126 degrees on Saturday

But the hottest temperatures compared to normal will center over the northern Rockies and Plains with highs soaring up to 105 degrees. That’s nearly 20 degrees higher than they should be.

Human-caused climate change is making heat waves like this one more likely to occur, as well as more intense and longer-lasting, studies show.

The heat dome responsible for this heat wave may also set records for its intensity in parts of Southern California and Arizona. Heat domes act like a lid on a pot, trapping and enhancing hot air beneath them. This one is expected to reach even higher in the atmosphere than typical, and that means it can trap even more air below it, raising the ceiling on just how extreme surface temperatures can get.

Heat is the deadliest type of extreme weather in the US, with a higher annual average death toll than tornadoes, hurricanes and lightning combined, National Weather Service statistics show.

This powerful heat dome is the latest in a spate of heat- dome-associated heat waves that have affected the US and Europe simultaneously so far this summer. Particularly strong and slow-moving heat domes are also possibly becoming more common as the world warms, though this is an area of active research.

This weekend’s heat may just be the first wave of extreme temperatures from this heat dome as it settles in for the long haul, with more hot weather predicted in large parts of the West beginning on August 6.

Dangerous, record-setting heat

More than 12 million people across the Southwest, Mountain West and northern Great Plains are under a Level 4 of 4 “extreme” heat risk Saturday and Sunday. An additional 12 million people are under a Level 3 of 4 “major” heat risk.

Heat at this level will affect anyone without access to cooling and hydration, the National Weather Service warns. Emergency room visits for heat-related illness surge on “major” and “extreme” risk days, according to the weather service.

Overnight lows will also remain nearly 10 degrees above normal across these regions, offering little relief even after dark. This lack of a cooldown is especially dangerous as it gives the body less time to recover before the next day’s heat builds again.

Billings, Montana, is forecast to hit 106 degrees on Saturday, breaking its August record. The city recorded its hottest-ever temperature of 111 degrees just two weeks ago.

Salt Lake City may set an August record with a forecast of 106 on Saturday, on the heels of breaking its all-time record high earlier this month.

Phoenix and Tucson, Arizona, and Las Vegas are all expected to rise well above 110 degrees. In Maricopa County, home to Phoenix, there have been 40 confirmed heat-related deaths so far this year, county data shows, with months of summer heat still to come.

California will see highs between 5 to 10 degrees above average. Much of the state will reach 100 to 110 degrees, while Los Angeles and other coastal communities will see highs around 80 to 90 degrees.

Californians seeking relief at the beaches will also need to be cautious as large waves and “potentially deadly rip currents” from far offshore Hurricane Genevieve impact the southern portion of the state.

Lifeguards with the Los Angeles County Fire Department performed nearly 2,000 ocean rescues last week as millions visited area beaches, the department said in a post on social media.

Heat triggers a wave of worrying impacts

The heat wave is also worsening wildfire and water concerns across the West, particularly the parched Colorado River Basin.

Much of the river basin as well as higher elevations in central and Southern California saw below average snowfall this past winter. This heat will dry out the ground further, making the region more vulnerable to wildfires.

Other concerns center on water and energy supplies, given the beleaguered state of the river basin.

The combined water level of Lake Mead and Lake Powell, two of the biggest US reservoirs, is at a historic low and continues to drop.

These reservoirs, together with the river basin overall, provide water to tens of millions of people. The heat wave will only exacerbate the rate of evaporation and decline in water levels from these critical resources.

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