US cities brace for extreme heat wave over the weekend

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.

Heat waves develop over a period of days, and therefore don't evoke the same sense of urgency as, for example, severe thunderstorms and tornadoes. A heat wave is defined as a period of abnormally and uncomfortably hot and unusually humid weather. Typically a heat wave lasts two or more days.

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.