What is a Heat Burst?
A heat burst is a downdraft of hot, dry air that normally takes place in the evening or during the night. It is much rarer than a harsh thunderstorm. Therefore, the atmospherical preconditions must be exactly right for a heat burst to take place. Heat bursts generally occur after thunderstorms end.
Features of a heat burst:
- A thunderstorm has a very important role in activating heat bursts.
- The air must initiate its fall from a higher altitude.
- And the air uphill has to be very dry.
Precipitation descending into very dry air uphill will induce the air to chill by dormant heat absorption. When the conditions are such that the air flows at a very high altitude and is denser than the contiguous air, then it will gather speed towards the surface. With regard to a heat burst, all the precipitation that chilled the air uphill has been “aerified," or infused with air.
Consequently, the precipitation is no longer able to take up any more underlying heat. The impenetrable air then accelerates and warms up at a fast pace with a dry adiabatic descent rate density. The reason for a heat burst being a rare phenomenon is because it depends on the very high velocities of a downdraft. The velocity of a downdraft must be so high that the momentum of the sinking air offsets the fact that it is getting warmer in temperature and less dense than the air it is descending into.
The air in a heat burst is not only anomalously hot, but also very dry. Similar to other atmospherical processes, heat bursts have variable strengths. The strongest heat bursts may continue for a significantly longer time with temperatures reaching as high as 120 F, even halfway through the night. This exceedingly hot and dehydrated air can continue for a number of hours before temperatures become normal. Temperatures of 90 °F (32 °C) during heat bursts have been recorded and sometimes have been observed increasing by 20 °F (11 °C) or above in a few minutes. Heat bursts are also sometimes coupled with very powerful, even destructive, winds.
Meteorologist Mike Smith, from WeatherData writes: “A ‘downburst’ is a unique form of extreme winds unknown to meteorologists prior to 1977 when it was discovered by Drs. Ted Fujita and Horace Byers. While they can occur anywhere, the Dallas area has bitter experience with downbursts." Let us look at what these downbursts are!