Most of America’s Lower 48 states is bracing for an "unusually large, strong and long-lasting" heat dome, which the National Weather Service warns will drive temperatures to "significant and dangerous" levels.
The severe heatwave is set to begin this weekend and persist for at least a week, with some regions experiencing its effects through the end of the month, according to meteorologists.
Temperatures are forecast to soar 15 to 25 degrees Fahrenheit (8 to 14 degrees Celsius) above normal across many areas, including during nighttime hours. Elevated nighttime temperatures pose a particular threat to human health and complicate efforts to manage an already active wildfire season.
Daniel Swain, a climate scientist with University of California Agriculture and Natural Resources, described the impending event as "pretty remarkable." He added, "This is going to be a long duration, widespread and high-intensity heat event that’s going to affect millions of people for over a week."
A high-pressure dome, which effectively traps hot air like a lid while blocking cooling winds and rain, will initially settle over the Northern Plains. Its immense size means it will ensnare sweltering conditions across as much as two-thirds of the continental United States.
While the East Coast may initially be spared, the heat dome is expected to shift and expand, potentially stretching from coast-to-coast over the next 10 days or more.
Forecasters anticipate record triple-digit highs this weekend in Nevada, Utah, Colorado, Wyoming, Idaho, Montana, North Dakota, and South Dakota. The weather service predicts over 90 U.S. local temperature records will be tied or broken by Wednesday, with two-thirds of these being overnight heat records that impede the body's recovery from scorching days.
"Nights can be just as dangerous as days. If you don’t get heat relief at night, that’s going to spill out into your daytime experience and become extremely dangerous," warned Bob Henson, a meteorologist with Yale Climate Connections.
He emphasized the severity: "Heat is not to be played with. It’s just as dangerous as a tornado or hurricane that can kill you just as easily, just in a quiet and different way."
What distinguishes this heatwave, Swain noted, is its sheer scale and prolonged duration. While major heatwaves have recently afflicted Europe, the U.S. East Coast, and the Southeast, this new event is poised to impact any part of the United States that previously escaped the July heat.
Intriguingly, rain is likely to slip beneath the southern edge of the heat dome, dousing the U.S. Southeast. This could lead to a peculiar scenario, explained Climate Central meteorologist Shel Winkley: the Southeast might experience record-shattering nighttime heat due to added moisture and humidity, yet see below-normal daytime warmth. Record nighttime heat is predicted for Saturday in locations from Texas to Florida to North Carolina.
Forecasts indicate temperatures will not drop below 80 degrees Fahrenheit (27 degrees Celsius) overnight in Fort Lauderdale, Miami, Tampa, Galveston, and Charleston.
While heat domes are a common summer phenomenon, Winkley highlighted this one's exceptional strength, likely setting records for the amount of high pressure it contains. Its unusually northern position also makes it stand out. Its prolonged persistence is attributed to drought-stricken areas having less soil and air moisture, which typically slows atmospheric warming, Swain explained. This drier, hotter air then intensifies drought conditions and fuels further heat in a dangerous feedback loop, exacerbating wildfire risks already heightened by drought.
Though the recently formed El Nino is too nascent to significantly influence this heatwave, climate change, driven by the burning of coal, oil, and natural gas, is undeniably a factor, according to the three meteorologists. "We know that heat waves are becoming more intense, they’re lasting longer, they’re covering larger areas than they used to because of human-caused climate change," Swain stated. "And so when we see an event like this, we know there is at least a partial contribution by the long-term warming trend."
Climate Central's analysis, utilizing 20 different computer models, compares forecasts to conditions expected without greenhouse gas-induced warming via its Climate Shift Index. A vast 20,000-square-mile (52,000-square-kilometer) area, stretching from Southern California to northern Minnesota and home to 24 million people, will experience warmth reaching the highest level on this index this weekend. This signifies the heat is at least five times more likely due to climate change, mirroring findings for recent East Coast and Southeast heatwaves. Winkley concluded, "Using attribution science we know that those temperatures would be virtually impossible without the influence of climate change."