National Weather Service warns of extreme heat across the US

“Usually heat domes break down after a week, maybe two weeks,” meteorologist Matthew Cappucci tells TIME.

Increased humidity making summers feel hotter The number of days with very high heat index (+100°F) events is increasing in the Twin Cities because the atmosphere is getting more humid due to climate change. Humidity and high temperatures factor into the heat index, or how hot it actually feels.

The term "heat dome" is just another way of saying a large area of high pressure. This promotes sinking, warming air over a large area and will lead to numerous record high temperatures being set as well as the first heat wave for many in the Northeast.