William Gallus is an esteemed professor of atmospheric science at Iowa State University.
A heat dome is a phenomenon where a persistent region of high pressure traps and concentrates heat over a particular area. This heat dome can extend over multiple states and linger for days or even weeks, subjecting the people, crops, and animals below to sweltering and stagnant air that feels like an oven.
Heat domes are typically associated with the behavior of the jet stream, which is a fast band of winds high in the atmosphere that usually flows from west to east. Normally, the jet stream exhibits a wavelike pattern, fluctuating north and then south and then north again. However, when these meanders in the jet stream become larger and slower, they can become stationary, leading to the formation of heat domes.
When the jet stream swings far north, air accumulates and sinks. As the air descends, it becomes warmer. This sinking air also reduces humidity, resulting in clear skies. These conditions allow the sun to intensify the heat near the ground.
If the air near the ground passes over mountains and descends, it undergoes even more warming. This downslope warming played a significant role in the extreme temperatures experienced during the 2021 heat dome event in the Pacific Northwest, resulting in record-breaking temperatures in Washington and British Columbia.
The impact on humans
Normally, heat domes persist for several days in a specific location, but they can last longer and move, affecting neighboring areas over weeks. An example of this is the heat dome that caused the U.S. heat wave in June 2022, which gradually moved eastward.
On rare occasions, heat domes can be even more persistent. This was observed in the 1980 southern Plains heat dome, which led to the unfortunate deaths of thousands of people due to weeks of intense summer heat. Similar prolonged heat domes also occurred during the Dust Bowl years in the 1930s.
A heat dome can have severe impacts on people, as the stagnant weather pattern usually results in weak winds and increased humidity. These factors amplify the feeling of heat and make it more dangerous, as the human body does not cool down as efficiently through sweating.
The heat index, which combines temperature and humidity, is often used to communicate the danger by indicating the perceived temperature to most individuals. High humidity also reduces nighttime cooling, leaving people without air conditioning unable to find relief. This increases the risk of heat-related illnesses and fatalities. Additionally, temperatures are already elevated due to global warming.
The summer of 1995 witnessed one of the worst examples of the impacts of a heat dome with high temperatures and humidity in the U.S. Over a span of five days, an estimated 739 people lost their lives in the Chicago area.
This article is republished from The Conversation under a Creative Commons license.
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