The heat wave continues this week: These are the areas in the U.S. facing the highest temperatures from the heat dome

The National Weather Service has warned that much of the Eastern United States will be under a heat dome this week, potentially leading to record-breaking temperatures.

This intense heat marks one of the hottest starts to summer in years. In response, the East Coast city of Philadelphia has declared a Heat Emergency through Wednesday.

Extreme Heat Warnings have also been issued for Chicago and surrounding counties, with forecasts predicting temperatures as high as 105°F. The heat is expected to persist into the night, offering little relief for those exposed during the day. Similar warnings are in effect for the Milwaukee area.

But the heat doesn’t stop there. States across the Midwest—including Indiana, Ohio, and Michigan—as well as parts of the Eastern Seaboard from Maryland to New York, are also under Extreme Heat Warnings.

For the full up to date list on those under Extreme Heat Warnings issued by the National Weather Service, check the website as updates are frequently made.

What is a heat dome?

A heat dome is a wide area of high pressure that encourages persistent hot and dry conditions that last for days or weeks at a time, according to AccuWeather.

Heat domes are usually formed when the atmosphere traps hot ocean air like a dome, when there is a large area of high pressure in the middle layers of the atmosphere.

The dome traps the heat, instead of letting it rise. As the hot air is trapped, it becomes even hotter as it is warmed further by the sun. Heat domes are also stationary, so the area it covers tend to feel the high temperatures for an extended period of time.

Heat domes contract and expand throughout the day, and if you find yourself inside of it, you will suffer from the heat, per AccuWeather. They can also prevent cloud formation, thus lessening the chances of having rain to bring down temperatures.

What is a heat wave?

According to the National Oceanic and Atmospheric Administration, a heat wave is a period of unusually hot weather that lasts for two or more days.

The government agency says that temperatures have to reach levels beyond historical averages for a particular area to be classified as a heat wave. This weather phenomenon is usually a result of trapped air.

Heat waves can be caused by the presence of heat domes, but heat waves can occur without them.

The term “heat dome” is recognized and defined by the American Meteorological Society, while the National Weather Service is unlikely to use it, preferring instead to speak of “heat waves.”

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