Heat dome will blanket much of the US, with worrisome temperatures in
Midwest
[June 19, 2025]
By ISABELLA O'MALLEY
Summer will make a dramatic entrance in the U.S. this week with a heat
dome that will bring stifling temperatures and uncomfortable humidity to
millions.
The heat will be particularly worrisome this weekend across wide
stretches of Nebraska, Illinois, Wisconsin and Iowa, where forecasters
are warning of extreme temperature impacts.
This will be the first stretch of true summertime weather for many from
Midwest to the East Coast, said Tom Kines, a meteorologist at the
private weather company AccuWeather.
“A lot of those folks have been saying, where’s summer? Well, buckle up,
because it’s coming,” said Kines. The humid conditions will make places
that exceed 90 degrees Fahrenheit (30 degrees Celsius) feel as much as
20 degrees hotter, said Kines.
Heat dome forming
A heat dome occurs when a large area of high pressure in the upper
atmosphere acts as a reservoir that traps heat and humidity, said Ricky
Castro, a National Weather Service meteorologist in Illinois.
According to the NWS Weather Prediction Center, daytime temperatures
will be in the 90s Fahrenheit (30s Celsius) and overnight temperatures
will only drop to the mid-70s Fahrenheit (mid-20s Celsius) from the
Great Lakes to the East Coast during the heat wave that's expected to
last into next week.
Moisture blown northward from the Gulf of Mexico is fueling the muggy
weather, said Jacob Asherman, a Weather Prediction Center meteorologist.
This influx of Gulf moisture is fairly typical during late spring and
summer, he said.
The heat will be widespread into next week. On Friday, Denver could
reach 100°F (38°C), according to the weather service. Chicago
temperatures could reach 96 degrees (36°C) on Sunday. On Tuesday,
Washington, D.C., could see a high of 99°F (37°C) and New York Central
Park could reach 96°F (36°C).
Several states in the Midwest could see dangerous temperature impacts
over the weekend, according to a weather service measure that rates the
risk from zero to four. Parts of Nebraska and Kansas will be in the
highest category on the scale on Saturday, meaning that anyone without
effective cooling or sufficient hydration could face health risks. On
Sunday, Iowa, Wisconsin, Missouri and Illinois also see a category 4
rating.
High humidity makes it hard to cool down
Humidity is the amount of water vapor in the air, and the heat index is
what the temperature feels like when the humidity outside is factored
in, according to the weather service.
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Wyatt Seymore pours the last drops of liquid from a water bottle
into his mouth as he takes a break from unloading a stiflingly hot
trailer of fireworks outside Powder Monkey Fireworks ahead of the
opening of the stand, June 17, 2024, in Weldon Spring, Mo. (AP
Photo/Jeff Roberson, File)
When humans sweat, it cools the body down because it absorbs and removes
heat as it evaporates off the skin. The air is saturated with water on
humid days, which makes it harder for sweat to evaporate. Hot and humid
days can be dangerous when the body is unable to cool itself off and can
exacerbate pre-existing health conditions and even lead to heat stroke.
Minimizing direct sun exposure, wearing loose and light-colored
clothing, staying hydrated and spending time in air-conditioned spaces
are ways to cool down during extreme heat, according to the NWS.
Some parts of the U.S., such as Phoenix, Arizona, are famously hot
without the mugginess. Phoenix and nearby desert regions experience this
so-called “dry heat” due to being located far away from large water
bodies, mountains that block moist air masses and weather patterns that
bring scarce precipitation.
Sweat evaporates faster in dry climates compared to humid ones. This can
be dangerous because it is easy to underestimate how dehydrated you are,
according to Johns Hopkins University and Johns Hopkins Health System.
Even the crops "sweat"
In places such as Iowa, crops can affect the humidity in summer months.
Plants feel the effects of hot weather and some people in the Midwest
are familiar with “ corn sweat,” which is when crops move water to their
leaves and other surfaces so it can evaporate, according to the Ohio
State University.
Madison County, Iowa, farmer Ryan Marquardt said corn sweat is “not as
bad as a sauna, but it definitely would have a sauna effect. It’s humid
in there (the cornfield), so you’re gonna sweat.”
Cornfield contributions to the overall humidity are much lower compared
to the humidity winds carry from the Gulf of Mexico, according to OSU.
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Associated Press writer Jack Dura in Bismarck, North Dakota, contributed
to this report.
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