the.com/heat dome

means A stubborn zone of high pressure traps hot air over a region for days, pressing it down and keeping cooler air from moving in — so temperatures climb and stay climbed.

from Not an old word at all — it's a modern meteorological compound, built plainly from 'heat' plus 'dome,' describing the shape the high-pressure system makes as it bulges over a region like an upside-down bowl. It moved from weather-service jargon into everyday headlines mainly in the 21st century, as unusually severe and prolonged heat events made the phenomenon common enough to need a common name.