The U.S. is sweating out its third major heat dome in a month, with some 70 million people affected in an area stretching from roughly New Mexico to North Carolina, covering much of the South and part of the Midwest. This latest extreme weather is again raising the risk of heat-related illness, particularly for millions of people in the affected region who lack easy access to air conditioning.
Daytime temperatures are reaching the 100s in many places, with the "feels like" temperature or heat index — which factors in humidity — even higher.
A heat dome is defined as a large, high-pressure atmospheric system that acts as a lid to trap hot air and humidity over an area for days or even weeks. "It's just a very strong area of high pressure. Under that, there's sinking air. Sinking air compresses, it warms, it heats up, and it also dries the air out," according to AccuWeather meteorologist Reneé Duff.
The heat dome will move west
Later in the week, "the main core of heat [is] shifting a bit farther west" with most of the 90-degree heat shifting to California and parts of the Four Corners region, Duff says. Friday, Saturday and Sunday will see record or near-record temperatures of about 115 degrees around Phoenix, she says.
"A lot of states that are being impacted by the highest temperatures are in severe to extreme drought," she adds. They include New Mexico, Colorado, Utah, Wyoming and Idaho, Duff says, where "the drier ground lends to higher temperatures."
Marc Chenard, a National Weather Service meteorologist, says the extreme heat advisories and warnings that remained in effect through at least Tuesday were concentrated in Arkansas, Tennessee and parts of the Gulf Coast.
He acknowledges that the intensity of these heat waves is unusual, with a prime factor likely being El Niño, the cyclical warming of the Pacific Ocean that increases the odds of warmer temperatures in North America.
"Typically we'll have a couple of these and they may kind of move around through the summer," Chenard says. "But, each one of these has been pretty strong, like the strength has been pretty impressive, and so just the persistence and strength certainly seems anomalous."
Research shows that climate change, due in large part to the burning of fossil fuels, is making heat waves hotter and more frequent.
According to a survey conducted last year by researchers at George Mason University and Yale, 65% of Americans are at least "somewhat worried" about global warming, including 29% who say they are "very worried." A separate survey published in May by the Pew Research Center found that Americans believe the worst impacts of climate change are unavoidable. It also found that while Democrats were more likely to be concerned about climate change than Republicans, nearly half of younger Republicans said the government isn't doing enough to combat the problem.
The latest U.S. heat wave comes as France and Spain are battling wildfires fueled by similar conditions in Europe.
A new analysis published by the research organization Climate Central found that, on average, people around the world lose about seven full nights of sleep each year due to uncomfortably warm temperatures.
People with heart disease or high blood pressure could be particularly vulnerable to the heat because some medications to treat those conditions interfere with the body's ability to manage excessive heat. A higher body mass index also increases the risk of heat stroke, experts say. Overweight people "heat up faster and they cool down slower," according to Douglas Casa, CEO of the sports medicine Korey Stringer Institute at the University of Connecticut.
Nighttime temperatures are rising faster than daytime temperatures and nights that never really cool off are also a concern, because the body never gets a chance to recover from those daytime highs, he says. This is especially true during a prolonged heat wave.
"The prolonged exposure to the heat ... can increase that risk," he says. People may become "progressively more dehydrated," and fatigued from poor sleep, he explains, while "your body temperature might not be coming down during recovery periods because it's hot where you're sleeping."
The basics of preventing heat stroke come down to common sense, Casa says: Stay out of the sun as much as possible. Drink lots of water or a drink with electrolytes. Wear light-colored, loose-fitting clothing. Take frequent breaks.
Cool first. Transport second
Warning signs of heat stroke include dizziness, headache, nausea, severe fatigue, and can include confusion, combativeness or potential loss of consciousness, Casa says.
Quick intervention before an ambulance arrives is key to keeping someone alive, he says. The best option is to immerse a heat stroke victim in cold water. "Cool first, transport second," he says.
On average, a heat stroke victim's core body temperature is 108 degrees. "We have a 30-minute window to get people's temperature under 104 to assure survivability," Casa says.
And unless heat stroke is properly treated, organ damage can occur that would make someone vulnerable to future heat injuries. "It's not just about surviving. It's also about surviving without long-term complications," Casa adds.
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