What Is a Heat Dome?

Written by Alice Twu, Rachel Reiff Ellis
Medically Reviewed by Neha Pathak, MD on July 01, 2026

Climate change has led to various weather phenomena in recent years. One of these is the increasing prevalence of heat domes. 

Heat domes occur when hot ocean air gets trapped in a specific area under a lid or cap. Climate change makes droughts worse and warms the atmosphere, which intensifies heat waves and causes them to last for an extended period. Heat domes are more likely to occur and stay longer when heat waves are more prevalent. As temperature rises in many parts of the world, heat domes are expected to become more frequent and deadly.

A heat dome occurs when hot ocean air is trapped over a large area. High atmospheric pressure over the region pushes air down, causing it to heat up as it is compressed. This action causes the formation of a “lid” or “cap” that seals heat in the area and traps heat in the dome. The heat dome effect causes the area trapped in the dome to experience a tremendous rise in temperature. 

A heat dome can affect large areas, even stretching over several states, and linger for days and up to weeks. People, plants, and animals stuck in the dome all suffer from the scorching temperature that can feel like being in an oven.

Heat domes result from a change in air temperature as it passes over land. It most commonly occurs when the temperature of the tropical Pacific Ocean rises in the winter, causing the air that passes over the water to also increase in temperature. As the warmer air that passes over the ocean travels from west to east, it gets trapped on land and forms heat waves. 

You can think of the Pacific Ocean as a huge pool being heated by heater jets. The distribution of warm water is not very even, as water closer to the jets is heated first compared to water farther away. As a result of climate change, the temperature of the western Pacific Ocean is higher than that of the eastern Pacific. The temperature difference leads to warm air rising higher over the western Pacific and pushing the colder air down over the eastern Pacific. As a result, more hot air passes across the land.

Usually, the wind passing from west to east travels in a wavelike pattern, going north and then south and then north again. The change in air temperature causes the meandering to become more prominent, causing the air to move slower or even become stagnant. That strong, high-pressure atmospheric conditions cause heat domes to occur.

A heat dome traps hot air in a large area in a dome-like manner. Hot air cannot escape through the top of the dome because of a cap-like formation caused by the high atmospheric pressure. The pressure causes the warm air to sink and compresses it, causing more heat to build. The hot air warms the ground and further heats the air above it. 

The problem with the high pressure is that the already warm or hot air trapped in the dome will become hotter and hotter. Hot air typically rises into the atmosphere, but the dome’s lid causes the air to sink. As the air sinks, it compresses and becomes warmer. That causes the temperature in the dome to rise continually. The hot air also warms the ground, causing moisture loss and making it even easier for the ground to heat more.

Heat domes are dangerous for humans, crops, and animals. They can lead to record-high temperatures during the day and warm temperatures to linger even through the night. Heat domes are even more dangerous for children, the elderly, and people with health conditions. 

High temperatures can cause various heat-related problems, such as heat rash, heat stroke, and fainting. Watch for symptoms like heavy sweating, dizziness, and nausea to prevent conditions from worsening.

Previous heat dome examples include one in the Chicago area in the summer of 1995 that caused an estimated 739 people to die over five days. In the summer of 2021, heat waves and heat domes affected the Northwest region of the United States and British Columbia. There were 100 heat-related deaths in Washington state alone. The extreme heat caused over 250 deaths in the U.S. and more than 400 in Canada.

Intense heat impacts everyone, but certain people may be at increased risk of sickness or more serious effects in a heat dome. People without access to air conditioning are especially vulnerable, especially if other ways to cool off (water to drink, cool showers) aren’t available. 

People who work outside and athletes who train outdoors should take special precautions when a heat dome is in effect. If you live with chronic conditions such as heart disease, poor blood circulation, or obesity, or if you’re pregnant, your risk of heat-related illness goes up. Your condition may make your body hold on to more heat than usual, make you less aware of temperature changes, or the medications you take may make heat effects worse.

Adults over 65 can have a harder time with temperature regulation and are more likely to live with chronic conditions and take medications that raise the risk of heat-related illness. These medications include: 

  • Diuretics (water pills)
  • Cardiovascular medications 
  • Nitrates
  • Antidepressants (mood stabilizers, antipsychotics, SSRIs, SNRIs, TCAs)
  • Antihistamines
  • Antiseizure medications
  • NSAIDS, aspirin
  • Antibiotics (sulfonamides)
  • Antiretrovirals (indinavir)
  • Thyroid medications (levothyroxine)

Other substances can raise your risk of heat-related illness. These include stimulants, including cocaine, amphetamines, and methylphenidate, hallucinogens such as MDMA, and alcohol.

Take special care with infants and young children in extreme heat conditions. Pay attention to their environment to be sure they are cool and hydrated when temperature and humidity is high. 

When it’s hot, keep your body cool by wearing lightweight, loose-fitting, breathable fabrics. Drink  plenty of fluids throughout the day. Drape a damp towel around the back of your neck or mist your skin and clothes with water. You lose salt and minerals (electrolytes) along with water when you sweat, so make sure to snack or drink sports drinks that replace these nutrients. 

Stay indoors during the hottest parts of the day (from around noon to 4 p.m.) and watch for signs of dehydration: 

  • Feeling very thirsty
  • Going long stretches without peeing
  • Dark-colored pee
  • Feeling tired, dizzy, or confused
  • Sunken eyes and cheeks

Try to take it as easy as possible during the hottest parts of the day. Try to do things like running errands and exercising before or after the midday hours. If you have to be outside during that time, be sure you have access to shade and fluids when you need them. 

It’s also important to recognize when heat is causing a medical problem, such as heat exhaustion or heat stroke. Know the signs:

Heat exhaustion can cause:

  • Dizziness and feeling faint
  • Lots of sweat
  • Cold, clammy skin
  • Nausea or vomiting
  • Rapid, weak heartbeat 
  • Muscle cramps

Heat stroke signs include:

  • Bad headache
  • Confusion
  • Red, hot, dry skin
  • High body temperature
  • Nausea or vomiting
  • Rapid, strong heartbeat 
  • Becoming unconscious

A heat stroke is a medical emergency. Call 911 if you or someone around you has these symptoms. 

Due to climate change, more heat domes are likely to occur and last for a longer time. People must prepare for this change in the weather pattern, especially in areas more prone to heat waves and heat domes. 

Short-term solutions include staying indoors as much as possible during a heat wave. For those who can, it may be tempting to run your air conditioning all day to keep cool. However, doing so can put a strain on the electric grid that may cause rolling brownouts or blackouts for everyone.

Instead, try to cool your house naturally as much as possible. Open your windows early in the morning or later in the evening when it’s not as hot outside to allow cool air in. During hotter times of the day, close your windows and draw your shades to keep the cool air in. 

If you need to go out, wear sun protection, such as sunscreen at least 30 SPF, sunglasses, and a hat or umbrella. Try to stay in the shade whenever possible, and drink plenty of water to stay hydrated.

Larger-scale solutions include planting more trees and building infrastructure to provide shade. Architects and engineers can design new buildings that can better withstand extreme heat. Electric companies can prepare backup plans for when more people will need the electric grid to lower the likelihood of brownouts or blackouts. You can also take action to reduce greenhouse gas emissions that cause climate change.

Add WebMD as a Preferred Source to see more of our trusted content across Google Search, AI Overviews, and AI Mode