Heat burst

In meteorology, a heat burst is a rare atmospheric phenomenon characterized by gusty winds and a rapid increase in temperature and decrease in dew point (moisture). Heat bursts typically occur during night-time and are associated with decaying thunderstorms.

Although this phenomenon is not fully understood, it is theorized that the event is caused when rain evaporates (virga) into a parcel of cold dry air high in the atmosphere making the air denser than its surroundings. The parcel descends rapidly, warming due to compression, overshoots its equilibrium level and reaches the surface, similar to a downburst.

Recorded temperatures during heat bursts have reached well above 38 °C (100 °F), sometimes rising by 11 °C (20 °F) or more within only a few minutes. More extreme events have also been documented, where temperatures have been reported to exceed 120 °F (49 °C). However, such extreme events have never been officially verified. Heat bursts are also characterized by extremely dry air and are sometimes associated with very strong, even damaging, winds.

In general, heat bursts occur during the late spring and summer seasons. During the late spring and summer seasons, thunderstorms tend to generate day heating and lose their main energy during the evening hours. Due to a potential temperature increase, heat bursts normally occur at night. In rare cases, heat bursts have been recorded to occur during the daytime as well. Heat bursts have lasted for times spanning from a couple of minutes to several hours. The rare phenomenon is usually accompanied by strong gusty winds, extreme temperature changes, and an extreme decrease in humidity. They occur near the end of a weakening thunderstorm cluster. Dry air and a low-level inversion are also present during the storm.

As the thunderstorm starts to dissipate, the layer of clouds start to rise. After the layer of clouds rise, a rain-cooled layer remains. The cluster shoots a burst of unsaturated air down towards the ground. In doing so, the system loses all of its up-draft related fuel. The raindrops begin to evaporate into dry air, which emphasizes the effects of the heat bursts. As the unsaturated air descends, the air pressure increases. The descending air parcel warms at the dry adiabatic lapse rate of approximately 10° Celsius per 1000 meters (5.5° Fahrenheit per 1000 feet) of descent. The warm air from the cluster replaces the cool air on the ground. The effect is similar to someone blowing down on a puddle of water. On 4 March 1990, the National Weather Service in Goodland, Kansas detected a system that had weakening, light rain showers and snow showers. It was followed by gusty winds and a temperature increase. A heat burst was being observed. The detection proved that heat bursts can occur in both summer months and winter months. The occurrence also proved that a weakening thunderstorm was not needed in the development of heat bursts.

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Wikipedia