Sweltering and humid conditions have impacted nearly the entire eastern U.S. this week, triggered by “heat domes” settling over various regions.

On Wednesday, a heat advisory impacted approximately 150 million individuals, with temperatures exceeding 95 degrees Fahrenheit spreading through the Ohio Valley and along the East Coast. The National Weather Service predicts that “extremely dangerous heat” will persist until Thursday.

But what exactly is a heat dome, and how does it contribute to extreme heat?

Heat domes form when a strong high-pressure system remains stationary over an area, trapping warm air underneath like a lid on a pot.

These thermal domes are typically influenced by the jet stream’s behavior. The jet stream is a fast-moving ribbon of air that flows from west to east in the Northern Hemisphere, impacting weather patterns.

The jet stream is powered by the temperature disparity between the chilly polar regions and warm southern air masses. As it travels around the globe, it can create ripples that form troughs and ridges, leading to unusual weather phenomena.

For instance, certain ripples can intensify cold snaps, while others can move and amplify heat, resulting in higher humidity levels.

Heat domes can persist for days or even weeks, contributing to prolonged heat waves that can be deadly. Heat-related illnesses and fatalities can impact individuals of all ages, but children, those with pre-existing health conditions, and older adults are especially vulnerable to sudden temperature spikes.

Research indicates that climate change is increasing the frequency, intensity, and duration of heat waves globally. The hottest years on record since 1850 have all occurred within the last decade, according to the National Oceanic and Atmospheric Administration.

Some respite is anticipated later this week across the Midwest and East Coast, although temperatures are expected to remain high in the days ahead.