Video: What Is a 'Heat Dome'? Everything You Need to Know

When the right conditions align, a weather phenomenon called a "heat dome" envelops the country, resulting in sizzling temperatures that last for days.

"A heat dome is the result of a couple of factors that are coming together. You've got your jet stream that is usually very, very far to the north into Canada," said NBC News meteorologist Sherri Pugh. "You have a building ridge south of the jet. That area acts as a dome, and then under this dome, you have a lot of sinking air. Sinking air is compressed and therefore it warms, and that adds an excessive amount of heat in the dome."