A heat dome is caused when the atmosphere traps hot ocean air as if bound by a lid or cap. The extensive dome traps warm air at all levels underneath, with layers sinking toward the ground. Strong high-pressure atmospheric conditions develop for an extended period, preventing convection and precipitation and leading to dry weather conditions.
The high pressure from the Earth’s atmosphere pushes the warm air down, compressing it. As its net heat is now in a smaller volume, it gets hotter. As the warm air attempts to rise, the high pressure above it forces it down, making itotter, and its pressure grows higher.
This leads to a dome-shaped area of hot air that can persist for several days or weeks. The high pressure acts as a dome, causing everything below it to get hotter and hotter.
Due to climate change, heat domes have become more frequent and intense. They usually cause dangerous heat waves, which can cause temperatures to climb to extremes.
High-pressure systems often bring clear skies, meaning the sunlight is less reflected, and heat is more absorbed with a lot of land and relatively dry air, such as plains and deserts, which also favor the formation of heat domes.
Heat domes can also lead to drought conditions and wildfires, as hot and dry weather quickly dries out vegetation and makes it more susceptible to fire.
What is a Heat dome, and why does it bring long-lasting heatwaves and excessive temperatures?
When significant and historic, record-breaking heat waves occurred in Europe, the United States, and Canada in the past, the Heat Dome was the cause. The heat dome is usually the dominant feature of summer weather patterns on both continents.
When extremely high temperatures develop, we will use the term heat dome. Here is how it works and why it is essential to understand it on a larger scale.
The upper-level ridge pattern, or very warm air mass in the higher altitudes, also known as the Upper High (or blocking High), usually forms the heat dome. This weather pattern brings very high and sometimes record-challenging temperatures to the region underneath.
This term is used when a broad area of high-pressure parks over a large portion of the continent. If the event is remarkably stable and extreme, it usually lasts several days or weeks.
The heat dome works like a lid on a pot. The extensive dome traps warm air at all levels underneath, with layers sinking toward the ground. Therefore, the air mass becomes anomalously warm at the lowest elevations and extremely hot near the surface.
The Omega blocking pattern
A heat wave associated with a heat dome creates fair, stable weather and an often arid air mass with minimal chances for precipitation or even clouds. This happens due to the sinking air parcels in the center of the heat dome, resulting in rising temperatures.
Note: The weather pattern that develops such extensive events is known as the Omega blocking High. Its shape reminds us of a letter in the Greek alphabet.
The example below shows a pattern that developed over Europe in September 2023. The omega-blocking pattern engulfs a large part of the continent, with a central heat dome and a low-pressure system on each side. In this case, one is over the southern Mediterranean, and the other is over the Azores.
Typically, warmer and drier weather leads to a significantly enhanced wildfire threat due to developing drought or worsening ongoing, preexisting, arid conditions. In recent years, wildfires have occurred in Europe (Portugal, Greece), the Pacific Northwest, and across Canada and North America.
Heat domes are often also to blame for deadly heat waves worldwide, as scorching and excessive heat lasts a long time. Such heat dome events brought record temperatures in many countries worldwide in the last few summer seasons, sometimes extending into the fall/autumn seasons.
The daily average and maximum temperatures under the heat dome are typically significantly above average. When the dome is mighty, it challenges or breaks existing historical records. This becomes particularly striking when this feature develops during early summer or autumn/fall.
How does a heat dome impact the life underneath?
Excessive heat in heat domes can significantly impact human health and be dangerous to particularly vulnerable populations, such as elderly individuals, children, and those with pre-existing health conditions that can be worsened by extreme heat.
Due to prolonged exposure to high temperatures, construction workers, farmers, and agricultural workers who work outdoors for long hours are at increased risk of heat-related illnesses. People living in poverty are also more susceptible to the fatalities of heat domes, as their houses are often built with heat-trapping surfaces such as concrete and asbestos.
Heat exhaustion occurs upon exposure to high temperatures for extended periods. It leads to dehydration, dizziness, and, in more severe cases, heat exhaustion can progress to a heat stroke.
High relative humidity during a heatwave can also significantly affect the body. For this reason, we use a Heat Index to represent the natural feel of scorching hot temperatures and high humidity. These graphics indicate the natural feel of temperatures based on the temperature and humidity.
As we see, when air mass has a temperature around +35 °C, humidity below 60 percent is much less challenging than once the humidity is very high, e.g., above 80 %. Thus, the actual feel temperature would be near 50 degrees Celsius.
Heatwaves have also been associated with increased rates of heart attacks, strokes, and respiratory illnesses.
Further details on the health risks can be found in our additional article: Health risks during a heatwave and sweltering hot weather
In addition to impacts on human health, heat domes can also significantly affect the environment due to more frequent droughts and wildfires combined with the overall warming climate. A combination of hot and dry conditions with reduced rainfall and increased evaporation rates leads to devastating consequences.
Heat domes can also damage infrastructure, such as roads and buildings, mainly if they are not designed to withstand such conditions.
Washingtonpost provided images used in this article.