Dangerously hot and humid conditions are choking nearly the entire eastern half of the United States this week, caused by a “heat dome” that’s parked over parts of the country.
Heat alerts were in effect Wednesday for around 150 million people. Temperatures over 95 degrees Fahrenheit were widespread across the Ohio Valley and through the East Coast. “Extremely dangerous heat” is expected to persist through Thursday, according to the National Weather Service.
But what is a heat dome, and why does the phenomenon bring oppressive heat with it?
A heat dome occurs when a strong and persistent region of high pressure sits over land and traps hot air, like a lid on a pot.
Heat domes are usually affected by the behavior of the jet stream, a ribbon of fast-moving air high in the atmosphere that flows from west to east in the Northern Hemisphere and affects weather systems.
The jet stream is fueled by temperature differences between the colder polar region to the north and warmer air masses to the south. As the jet stream flows around the planet, it can ripple in places, creating troughs and ridges that often result in unusual weather patterns.
Certain ripples can, for instance, amplify cold snaps. Others can move hot air over land, blasting heat and intensifying humidity.
Heat domes can linger for days or weeks, fueling prolonged heat waves that can turn deadly. Heat-related illness and death can affect any person of any age, but children, people with pre-existing health conditions and the elderly are particularly susceptible when temperatures spike.
Climate change is also increasing the frequency, intensity and duration of heat waves around the world, studies have shown. The planet’s 10 hottest years since 1850 have all occurred in the past decade, according to the National Oceanic and Atmospheric Administration.
Some relief is expected later this week across the Midwest and throughout the East Coast, but heat and humidity are expected to remain high in the coming days.
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