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 southern California to Western 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. High temperatures will climb between 10 F to nearly 20 F degrees hotter than they should be - even for the peak of summer - from southern California to the northern Rockies and Plains from Friday through Tuesday. Death Valley, California, is forecast to see the hottest temperature of this heat wave: a blistering 126 F. This is the latest in a spate of record-breaking heat waves that have affected the U.S. and Europe simultaneously this summer. 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. 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. 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. 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, with an additional 12 million people 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. The weekend 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 Aug. 6. Dangerous, record-setting heat By Aug. 4, around 10 per cent of the continental U.S. will record the hottest day of the year so far. Billings, Montana, is forecast to hit 106 degrees on Saturday, breaking its August record. The city recorded its hottest-ever temperature of 111 F 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. In California, where highs across much of the state will reach 100 to 110 F, anyone seeking relief at the beaches will need to be cautious: Far offshore Hurricane Genevieve will send large waves and rip currents along 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. Phoenix and Tucson, Arizona, and Las Vegas are all expected to rise well above 110 F. 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. Heat is the deadliest type of extreme weather in the U.S., with a higher annual average death toll than tornadoes, hurricanes and lightning combined, National Weather Service statistics show. 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 the West, 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. 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, spanning the southwestern United States and northwestern Mexico. 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 U.S. 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. By Meteorologist Tyler Ory and Andrew Freedman, CNN
