'A lid on a pot': How does a heat dome work?

A seven-day "HeatRisk" map from the National Integrated Heat Health Information System shows much of the eastern U.S. in the grip of a heat dome causing extreme high temperatures to linger.

"If you've made grilled cheese in a pan and you put a lid on there, it melts the cheese faster because the lid helps trap the heat," a National Weather Service official told NPR.

(Image credit: Esri, TomTom, Garmin, FAO, NOAA, USGS, EPA, USFWS)