The Science Behind the Heat Dome — ‘a Mosh Pit’ of Molecules

From Texas clear to Georgia, from the Gulf Coast on up to the Canadian border, a mass of dangerous heat has started spreading like an atmospheric plague. In the days and perhaps even weeks ahead, a high-pressure system, known as a heat dome, will drive temperatures over 100 degrees Fahrenheit in some places, impacting some 160 million Americans. Extra-high humidity will make that weather even more perilous — while the thermometer may read 100, it might actually feel more like 110.

So what exactly is a heat dome, and why does it last so long? And what gives with all the extra moisture?

A heat dome is a self-reinforcing machine of misery. It’s a system of high-pressure air, which sinks from a few thousand feet up and compresses as it gets closer to the ground. When molecules in the air have less space, they bump into each other and heat up. “I think about it like a mosh pit,” said Shel Winkley, the weather and climate engagement specialist at the research group Climate Central. “Everybody’s moving around and bumping into each other, and it gets hotter.”