More than 150 million Americans from Texas to Maine are under extreme heat advisories as dangerously high temperatures bake the nation. Meteorologists warn that this heat dome could expand to affect an additional 20 million people by mid-week.
In more than three dozen states from the Plains to New England, daytime temperatures could reach and exceed 100 degrees Fahrenheit (38 degrees Celsius) through at least Tuesday, AccuWeather reports. In an advisory issued Monday, June 23, the National Weather Service (NWS) said “extremely dangerous” temperatures should expand from the Midwest into the Mid-Atlantic and break “numerous” records, warning that the heat will be especially brutal in dense cities such as Columbus, Ohio; Philadelphia, Pennsylvania; and Washington D.C.
“Heat related illnesses increase significantly during extreme heat. Wear lightweight and loose fitting clothing. Take action when you see symptoms of heat exhaustion and heat stroke,” NWS officials advised.
As temperatures crept up over the weekend, multiple U.S. cities set daily record highs, The Weather Channel reports. That includes Mitchell, South Dakota, which broke its daily high temperature record at 104 degrees Fahrenheit (40 degrees Celsius) on Saturday, surpassing the previous record of 101 degrees Fahrenheit (38 degrees Celsius). That same day, high temperature records were set across Minnesota and Wyoming. And on Sunday, Marquette, Michigan, set a new high temperature record of 93 degrees Fahrenheit (34 degrees Celsius).
“It’s a little earlier than normal to get this type of heat,” AccuWeather senior meteorologist Adam Douty told Gizmodo. These temperatures usually hit in July or August, but this certainly isn’t the first time that the U.S. has seen stretches of 90-to-100-degree weather in June, he said. “We are setting records in some places, not by a lot.”
Heat domes form when a persistent region of high pressure traps heat over a particular area, elevating temperatures for days to weeks, according to the National Oceanic and Atmospheric Administration. They are typically linked to the behavior of the jet stream, a band of fast-moving winds high in the atmosphere that meanders in a wave-like pattern around the globe. When the jet stream creeps northward, it slows down and sinks, which lowers humidity. This allows the sun to heat up temperatures on the ground.
“The jet stream goes way to the North, up in Canada, and underneath that you have warm air at all levels of the atmosphere,” Douty explained. He expects this week’s heat dome to remain centered over the eastern third of the nation until Wednesday and for temperatures to begin falling by Thursday. “Certainly the second half of the week does show some relief,” he said.
Though this heat dome should be relatively short-lived, it will still pose significant health risks. Extreme heat exposure can induce potentially life-threatening illnesses such as heat stroke and rhabdomyolysis—the rapid breakdown, rupture, and death of muscle. What’s more, extreme heat can worsen many chronic conditions, including cardiovascular, mental, respiratory, and diabetes-related conditions.
Above-normal nighttime temperatures can be particularly dangerous, Douty said. Last night in New York City, for example, the temperature only dropped to around 80 degrees Fahrenheit (27 degrees Celsius). By 9 a.m. ET, it was already almost 90 degrees Fahrenheit (32 degrees Celsius). This increases the risk of heat-related illness.
“The body just doesn’t have a chance to recover whenever you have nighttime temperatures like that,” Douty said.
As the week progresses, a zone from New Mexico and western Texas up through the central Plains and Midwest—including states such as Nebraska, South Dakota, Iowa, Minnesota, and Wisconsin—could see multiple rounds of thunderstorms, according to Douty. The storms will result from the temperature gradient between the eastern heat dome and relatively cooler conditions in the West, he said. While this could reduce dangerously high temperatures in some areas, severe storm activity would introduce new hazards.
“There will be some severe weather in terms of damaging wind, hail, and maybe a couple of tornadoes,” Douty said. “Another thing we’re watching now is the heavy rain threat in parts of the Midwest, from eastern Nebraska into Iowa and Wisconsin. There could be multiple inches of rain in that area, and that could lead to some flooding,” he added.
Beginning Wednesday, thunderstorms are also expected to rumble into the heat dome’s northeastern periphery, affecting an area from the Great Lakes to the Northeast and the northern Mid-Atlantic, AccuWeather reported. While this should cool things down, temperatures are likely to remain in the 90s for most of the mid-Atlantic.
This early summer heatwave isn’t necessarily a sign that we’re in for a hotter-than-average summer, Douty said. Climate models, however, suggest that we are. The NWS Climate Prediction Center’s seasonal outlook for July, August, and September 2025 predicts above-average temperatures for the majority of the U.S. As global temperatures continue to rise, so will the frequency and intensity of extreme heat events.
