Extreme Heat Wave Engulfs the US

More than 150 Million Americans Under Extreme Heat Advisories

More than 150 million Americans, spanning from Texas to Maine, are currently under extreme heat advisories due to dangerously high temperatures that are baking the nation. Meteorologists warn that this heat dome could expand, affecting an additional 20 million people by mid-week.

Heatwave to Reach 100 Degrees Fahrenheit in Over Three Dozen States

In more than three dozen states, from the Plains to New England, daytime temperatures are expected to reach and exceed 100 degrees Fahrenheit (38 degrees Celsius) through at least Tuesday, according to AccuWeather reports. The National Weather Service (NWS) issued an advisory on Monday, June 23, stating that "extremely dangerous" temperatures will expand from the Midwest into the Mid-Atlantic, breaking numerous records. The heat is expected to be especially brutal in dense cities such as Columbus, Ohio; Philadelphia, Pennsylvania; and Washington D.C.

Precautions Against Heat-Related Illnesses

NWS officials advised taking precautions against heat-related illnesses, which increase significantly during extreme heat. They recommended wearing lightweight and loose-fitting clothing and taking action when symptoms of heat exhaustion and heat stroke are seen.

Record-Breaking Temperatures Across the US

As temperatures rose over the weekend, multiple US cities set daily record highs, The Weather Channel reports. This 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). High temperature records were also set across Minnesota and Wyoming, and on Sunday, Marquette, Michigan, set a new high temperature record of 93 degrees Fahrenheit (34 degrees Celsius).

Early Onset of Extreme Heat

AccuWeather senior meteorologist Adam Douty noted that it’s a little earlier than normal to experience this type of heat, which usually occurs in July or August. However, this isn’t the first time the US has seen stretches of 90-to-100-degree weather in June, and records are being set in some places, albeit not by a lot.

Formation of Heat Domes

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. This is 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, lowering humidity and allowing the sun to heat up temperatures on the ground.

Expected Duration and Relief of the Heat Dome

Douty explained that the jet stream has gone far north into Canada, and underneath it, there is warm air at all levels of the atmosphere. 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.

Significant Health Risks

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. Moreover, extreme heat can worsen many chronic conditions, including cardiovascular, mental, respiratory, and diabetes-related conditions.

Danger of Above-Normal Nighttime Temperatures

Above-normal nighttime temperatures can be particularly dangerous, Douty said. For example, last night in New York City, the temperature only dropped to around 80 degrees Fahrenheit (27 degrees Celsius), and by 9 a.m. ET, it was already almost 90 degrees Fahrenheit (32 degrees Celsius). This increases the risk of heat-related illness.

Lack of Recovery Time for the Body

"The body just doesn’t have a chance to recover whenever you have nighttime temperatures like that," Douty said.

Thunderstorms and Severe Weather

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. While this could reduce dangerously high temperatures in some areas, severe storm activity would introduce new hazards.

Severe Weather, Damaging Winds, and Flooding

"There will be some severe weather in terms of damaging wind, hail, and maybe a couple of tornadoes," Douty said. Another thing being watched 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.

Cooling Down but Remaining Hot

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.

Early Summer Heatwave and Predictions for a Hotter Than Average Summer

This early summer heatwave isn’t necessarily a sign that we’re in for a hotter-than-average summer, Douty said. However, climate models 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 US. As global temperatures continue to rise, so will the frequency and intensity of extreme heat events.