Imagine waking up at midnight to find the temperature has shot up 20 degrees in minutes and 80 mph wind gusts have ravaged your town. Though a rare phenomena, that’s the power of a heat burst.
Heat bursts occur in the wake of dying thunderstorms, but other conditions have to be just right — the storm has to be high in the atmosphere and the air beneath must be hot and dry. When the storm rains into this arid environment, the water quickly evaporates. Evaporation takes heat energy out of the surrounding air and causes it to cool and contract, so we end up with a very dense parcel of air too heavy to stay up. It begins to fall through the atmosphere, and the quicker it’s losing heat, the quicker it falls.
Normally, moisture is still evaporating while it descends. This offsets the heating that happens as the falling air is squished by the layers of air above it. But in the case of a heat burst, all of the moisture evaporates and that dense air is only getting warmer as it approaches the ground at high speeds. When it hits, it suddenly delivers oppressively hot and dry air that can stay in place for hours.