Twitter Map: Geopotential Height of Heat Dome on July 6, 2018

The intensity of heat domes is evaluated using a measure known as “geopotential height,” which is the height in the atmosphere at which 500 millibars of pressure occur. The higher this pressure level is, the hotter it is, because hot air is less dense than cold air and fills more space. The most intense heat domes, which are extraordinarily rare, feature geopotential heights exceeding 6,000 meters at their core.

The heat dome on July 6, 2018 exceeded the 6,000-meter geopotential height threshold in several locations in the Western United States and was nearly that high (5,940 meters or higher, as shown within the red outline in the image below) over a sprawling area from Southern California to southern New England.