The following essay is reprinted with permission Conversationan online publication covering the latest research.
A heat dome occurs when a persistent area of high pressure traps heat in an area. A heat dome can span several states and linger for days to weeks, leaving people, crops and livestock below suffering from stagnant hot air that can feel like an oven.
Generally, heat domes are tied to behavior jet streama band of fast winds high in the atmosphere that usually runs from west to east.
Normally, the jet has a wavy pattern, winding north, then south, and north again. As these jet meanders become larger, they move more slowly and may become stationary. That’s when heat domes can occur.
As the jet swings far north, air accumulates and sinks. The the air heats up as it descends, and the downdraft also keeps the sky clear as it reduces humidity. This allows the sun to create increasingly hot conditions near the earth.
When air near the ground passes over mountains and descends, it can warm even more. This warming played a large role in the extremely high temperatures in the Pacific Northwest during a heat dome event in 2021when Washington set a state record of 120 degrees Fahrenheit (49 degrees Celsius), and temperatures reached 121 F in British Columbia, Canada, surpassing the previous Canadian record by 8 degrees F (4 C).
Heat domes usually last for a few days in any location, but they can last longer. They can also move around, affecting neighboring areas within a week or two. The heat dome that was involved in the June 2022 US heat wave has crept eastward over time.
In rare cases, the thermal dome may be more stable. It happened in the village southern plains in 1980, when about 10,000 people died in several weeks of intense summer heat. It also happened in most of the United States during the Dust Bowl years 1930s.
A heat dome can have serious consequences for humans because the stagnant weather that allows it to exist usually results in low winds and increased humidity. Both factors worsen the feeling of heat – and become more dangerous – because the human body does not cool down as much from sweating.
The heat index, a combination of heat and humidity, is often used to convey this danger by indicating what temperature most people will feel. High humidity also reduces the amount of night cooling. Warm nights can leave people without air conditioning unable to cool themselves, increasing the risk of heat illness and death. With global warming, the temperature is already highertoo.
One of the worst recent examples of heat dome strikes with high temperatures and humidity in the US occurred in the summer of 1995when evaluated 739 people died in the Chicago area more than five days.