What’s a Heat Dome? Here’s the Scoop on That Sizzler
Published Jul 23, 2025
A heat dome is a persistent, high-pressure system aloft that acts like a lid—compressing air, trapping heat, preventing clouds and rain. This intensifies ground-level temperatures and sustains dangerous heat waves over days to weeks. Currently, a heat dome is parked over much of the U.S., pushing heat indices above 100 °F, exacerbated by humidity in the Corn Belt.
Heat dome traps hot air like a lid
Imagine a giant, invisible lid placed over a region, trapping hot air and preventing it from escaping. That's essentially what a heat dome does. It's a persistent high-pressure system in the upper atmosphere that acts like a lid, compressing the air below. This compression causes the air to heat up, leading to scorching temperatures at ground level.
High-pressure system forces air downwards, warming it
The high-pressure system forces air downwards. As this air sinks, it warms up. This warm air then gets trapped near the surface, because the high-pressure system prevents it from rising and dispersing. The result is a prolonged period of intense heat, often accompanied by high humidity, making it feel even hotter.
Lasts days or weeks, prevents cloud formation
Heat domes can last for days or even weeks, turning what might have been a normal summer heat wave into a dangerous and potentially deadly event. They also tend to prevent the formation of clouds and rainfall, further exacerbating the heat and dryness. The lack of cloud cover means the sun's rays beat down relentlessly, adding to the already intense heat.
U.S. heat index well above 100°F
The current heat dome parked over much of the U.S. is a prime example. It's pushing heat indices—what the temperature feels like when you factor in humidity—well above 100°F (38°C) in many areas. The Corn Belt, known for its agricultural productivity, is particularly affected due to the high humidity levels, making the heat feel even more oppressive.
Climate change makes heat domes more frequent
While natural variations in weather patterns play a role, many scientists believe that climate change is making these events more frequent and intense. As the planet warms, extreme weather events like heat domes are likely to become more common, posing a significant threat to public health and agriculture.
Essential tips to protect from heat dome
Here are a few essential tips:
Drink plenty of water throughout the day
Drink plenty of water throughout the day, even if you don't feel thirsty.
Avoid prolonged exposure to direct sunlight
Avoid prolonged exposure to direct sunlight, especially during the hottest parts of the day (usually between 10 a.m. and 4 p.m.).
Spend time in air-conditioned environments
Spend time in air-conditioned environments, such as shopping malls, libraries, or community centers. If you don't have air conditioning at home, consider visiting a cooling center.
Wear loose-fitting, light-colored clothing
Wear loose-fitting, light-colored clothing.
Avoid strenuous physical activity during hottest times
Avoid strenuous physical activity during the hottest parts of the day.
Check on vulnerable neighbors, friends, relatives
Check on elderly neighbors, friends, and relatives who may be more vulnerable to heat stress.
Car temperatures reach dangerous levels quickly
Even on a relatively mild day, the temperature inside a car can quickly reach dangerous levels.
Understand heat domes, protect ourselves, communities
Heat domes are a serious weather phenomenon that can have significant impacts on our health and well-being. By understanding what they are and how they work, we can take steps to protect ourselves and our communities during these extreme heat events.
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