Understanding heat domes and what causes them as many regions in the world face extreme heatwave

On Tuesday, tens of millions across the United States grappled with oppressive heat as summer set in with a vengeance. The US National Weather Service reported that a significant heatwave is impacting large parts of the Ohio Valley, Great Lakes, Northeast, and Mid-Atlantic regions this week. This heatwave is expected to bring widespread daily record-high temperatures and warm overnight lows, with some monthly records potentially being broken, the weather agency said. Heat index readings are anticipated to peak between 100 and 105 degrees Fahrenheit in many areas, making conditions particularly dangerous for those without reliable air conditioning. The persistently high overnight temperatures will prevent natural cooling, leading to increased heat risk indoors for those without air conditioning.

The surge of extreme heat before the official start of summer has caught many off guard. Last year, the United States experienced the highest number of heatwaves—defined as abnormally hot weather lasting more than two days—since 1936, according to an Associated Press. With the Midwest and Northeast currently enduring or on the brink of extreme summer heat, meteorologists are increasingly discussing phenomena such as heat domes.

Understanding Heat Domes

A heat dome occurs when a high-pressure system forms in the upper atmosphere, causing the air below it to sink and compress, thereby raising temperatures in the lower atmosphere. This process creates a bulging dome of hot air. According to atmospheric science expert a heat dome describes atmospheric conditions while a heatwave is the ground-level impact felt by people. The boundaries of the current heat dome are not well-defined, indicating the widespread nature of this heat event.

What Constitutes a Heatwave?

Meteorologist Jeff Masters of Yale Climate Connections explains that a heatwave is characterized by the intensity of the heat, its duration, and its geographic location. The combination of clear skies and the higher angle of the summertime sun can lead to high heat index readings, which are a measure of temperature combined with humidity. Humidity exacerbates the feeling of heat because it hampers the body's ability to cool itself through sweating, making the weather feel hotter.

Record-Breaking Heatwaves

Last year, the U.S. experienced the highest number of heatwaves since 1936. An analysis by the Associated Press of data from the Centers for Disease Control and Prevention revealed that excessive heat contributed to over 2,300 deaths in the U.S., the highest number recorded in 45 years.