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More than 170 million Americans will face dangerous temperatures and humidity in the coming days as a heat dome develops over much of the U.S.
The first major heat wave of the year is expected to challenge record temperatures across the central and eastern states from the weekend into next week.
“It will be exceptionally warm at night with little relief once the sun goes down," AccuWeather Chief On-Air Meteorologist Bernie Rayno warned. "Many urban areas may struggle to drop below 80 at night, and that can take a toll on the body without air conditioning."
Sweltering heat was already impacting the West on Thursday and Friday – the longest day of the year – with highs peaking up to 104 degrees around Salt Lake City and Denver. One picture shared by the National Weather Service in Utah captured an infrared thermometer reading on a car’s dashboard at 165 degrees.
“NEVER leave children or pets inside a closed car on a hot day like this,” they said.
So, what is a heat dome, how does it form, and what should Americans be wary of in the upcoming days? Here’s what to know...
What is a heat dome?
A heat dome occurs when a large area of high pressure in the upper atmosphere acts as a reservoir that traps heat and humidity, Ricky Castro, a National Weather Service meteorologist in Illinois, said.
Warm surface air beneath a heat dome can linger for several days or even weeks, threatening human health.
Extreme heat is the leading cause of weather-related fatalities in the U.S.
“Extreme heat is tragically the leading cause of weather-related fatalities in America,” AccuWeather Chief Meteorologist Jonathan Porter said. “There is an amplified risk of heat-related illnesses because this is the first heat wave of the year for millions of people, and their bodies are not yet acclimated to this type of heat and humidity.”
How do they form?
Heat domes are typically linked to the behavior of the jet stream which, the National Oceanic and Atmospheric Administration explains, is a band of fast winds high in the atmosphere that move in meandering wavelike patterns. When the jet stream shifts northward, it moves slower and sinks. That allows for lower humdity and for the sun to create progressively hotter conditions on the ground.
However, air descending down mountains can also contribute to heat domes, as it warms even more.
Over cities, it is often warmer because pavement, buildings, and other types of hard surfaces tend to absorb and retain more heat.
“There may be more danger than a typical heat event, due to the longevity of near-record or record high nighttime lows and elevated heat index readings,” the National Weather Service’s Weather Prediction Center said.
Who will it impact this time?
Last summer, a heat dome “broiled” the Northeast and Midwest. This summer, it’s coming for big cities in the central U.S. and along the East Coast, along with horrible humidity that makes being outside even riskier.
AccuWeather expects that Philadelphia and Washington, D.C. will experience at least one week with highs at or above 90 degrees.
To the north, the Big Apple will also see multiple days of highs in the 90s, and areas around Manhattan will have temperatures exceeding 100 degrees.
Heading west, Chicagoans are bracing for three to five days of highs in the 90s, marking the “most intense heat wave Chicago has experienced in the last few years.”
Temperatures in Kansas City, Missouri, Oklahoma City, St. Louis, and Nashville will also leap above 90 degrees for multiple days.
To the Southeast, Atlanta and Charlotte are forecast to see temperatures between five and 15 degrees above the historical average.
So, how long will it last?
Temperatures are expected to dip a bit by mid-week and into the weekend, according to Fox Weather. Still, this is only the start of the summer season.
Human-caused climate change is making heat waves more frequent and severe. Last year was the hottest year on record, and the first heat advisory was issued in Alaska last week.
This will be the first stretch of true summertime weather for many in the eastern U.S.
“A lot of those folks have been saying, where’s summer? Well, buckle up, because it’s coming,” AccuWeather’s Tom Kines said.
With reporting from The Associated Press
