What is a heat dome? Explaining the weather phenomenon baking large parts of US | Weather

The first day of summer 2022 brought soaring temperatures across a large part of the United States. National Weather Service

A heat dome occurs when a persistent region of high pressure traps heat over an area. The heat dome can spread over several states and linger for days to weeks, leaving the people, crops and animals below suffering through stagnant, hot air that can feel like an oven.

Typically, heat domes are tied to the behavior of the jet stream, and a band of fast high winds in the atmosphere that generally runs west to east.

Normally, the jet stream has a wavelike pattern, meandering north and then south and then north again. When these meanders in the jet stream become bigger, they move slower and can become stationary. That’s when heat domes can happen.

When the jet stream swings off to the north, on piles up and sinks. The air warms as it sinks, and the sinking air also keeps skies clear since it lowers humidity. That allows the sun to create hotter and hotter conditions near the ground.

If the ground passes over mountains and descends, it can warm even more. This is the easiest temperature in the Pacific Northwest during a heat dome event in 2021, when Washington set a state record with 120 degrees Fahrenheit (49 Celsius), and temperatures reached 121 F in British Columbia in Canada, surpassing the previous Canadian record by 8 degrees F (4 C).

Map of US with a bubble over the Midwest showing arrows moving, with the ridge on sinkingHeat domes involve high-pressure areas that trap and heat up the air below. NOAA

The human impact

Heat domes usually persist for several days in any one location, but they can last longer. They can also move, influencing neighboring areas over a week or two. The heat dome involved in June 2022 US heat wave crept eastward over time.

On rare occasions, the heat dome can be more persistent. That happened in the southern Plains in 1980, when as many as 10,000 people died during high summer heat weeks. It also happened over much of the United States during the Dust Bowl years of the 1930s.

Because of the stagnant weather pattern that allows it to prevail in weak winds and increase in humidity. Both factors make the heat feel worse – and become more dangerous – because the human body is not cooled as much by sweating.

The heat index, a combination of heat and humidity, can often be used to indicate what the temperature will feel like to most people. The high humidity also reduces the amount of cooling at night. Warm nights can leave people without air conditioners, which increases the risk of heat illnesses and deaths. With global warming, temperatures are already higher, too.

The summer of 1995, when an estimated 739 people died in the Chicago area over five days.

William Gallus receives funding from the National Science Foundation.

This article is republished from The Conversation under a Creative Commons license.

departure from average temperature


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