Most of America’s Lower 48 states will swelter under an unusually large, strong and long-lasting heat dome that will spike temperatures starting this weekend and lasting at least a week, the National Weather Service said.
Daniel Swain, a climate scientist with University of California Agriculture and Natural Resources, said, "This upcoming heat wave does look pretty remarkable."
Three meteorologists said a dome of high pressure will initially park over the Northern Plains and could trap sweltering temperatures across as much as two-thirds of the continental United States.
Forecasters are expecting record triple-digit highs this weekend in Nevada, Utah, Colorado, Wyoming, Idaho, Montana, North Dakota and South Dakota.
The weather service is predicting more than 90 U.S. local temperature records will be tied or broken through Wednesday, with two-thirds being overnight heat records. "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," said meteorologist Bob Henson with Yale Climate Connections.
Temperatures are expected to be 15 to 25 degrees Fahrenheit (8 to 14 degrees Celsius) warmer than normal in many areas, including at night, which meteorologists said is especially bad for human health and for efforts to tamp down an already active wildfire season.
The weather service is predicting record nighttime heat in a number of locations from Texas to Florida to North Carolina on Saturday, and forecast temperatures won’t drop below 80 degrees at night in Fort Lauderdale, Miami, Tampa, Galveston and Charleston.
The El Nino that recently formed is too young to have a pronounced impact on this heat wave, but the three meteorologists said climate change from the burning of coal, oil and natural gas clearly does.
Climate Central uses 20 different computer models to compare what’s forecast to what would be expected in a world without greenhouse gas-caused warming, and found a 20,000-square-mile swath from Southern California to northern Minnesota where 24 million people live will have warmth reaching the highest level on its index, meaning the heat is at least five times more likely because of climate change. "Using attribution science we know that those temperatures would be virtually impossible without the influence of climate change," said Climate Central meteorologist Shel Winkley.
Rain is likely to sneak below the southern edge of the heat dome and douse the U.S. Southeast during the daytime, which could produce added moisture and humidity that leads to record-shattering nighttime heat while producing below-normal daytime warmth, Winkley said, and some areas could feel the heat’s effects until the end of the month.
"The heat doesn’t necessarily stop when it’s dark out," said Josh Adam, a meteorologist with the National Weather Service in Bismarck, North Dakota, where he said temperatures will surpass 100 degrees Fahrenheit (37 degrees Celsius) until Tuesday.
Chad Merrill, a senior meteorologist with AccuWeather, said the current heat dome is one of the strongest to affect the Dakotas in 25 years and warned that dry thunderstorms could develop across the Rockies, raising fire risk in already dry areas.
Andrew Gorelow, a meteorologist with the National Weather Service in Las Vegas, said Nevada is even hotter than normal and that Las Vegas is expected to reach 111 degrees Fahrenheit (48 degrees Celsius) on Saturday.
In Helena, Montana, where temperatures were expected to creep above 95 degrees Fahrenheit (35 degrees Celsius), Last Chance Splash Waterpark & Pool held a swim meet for hundreds of swimmers. "It’s certainly a hot day, but the pool is nice and cool," said Sean Swingley, assistant manager, adding that Helena usually sees temperatures that hover around 85 to 90 in June and July.
The current El Nino formed last month and is expected to rank among the most intense since the weather service began tracking them in 1950, and the U.S. National Oceanic and Atmospheric Administration said it has an 81% chance of becoming "very strong," the top category, by fall.