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Characteristics of Heat Bursts

In general, heat burst occur during the late spring and summer seasons. During the late spring and summer seasons, thunderstorms tend to generate day heating and lose it's main energy during the evening hours. Due to potential temperature increase, heat burst normally occur at night. In rare cases, heat bursts have been recorded to occur during the daytime as well. Heat bursts have lasted in a time span of a couple of minutes to several hours at a time. 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 is also present during the storm.

What Causes Heat Bursts?

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 it's 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 pressure increases. The compression of pressure causes warming at the rate of 33.8 degrees Fahrenheit per 100 meters of height. 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. In March 4,1990, 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.

Heat Bursts is another variety of Microbursts and Downbursts.

Forecasting Heat Bursts

The first step of forecasting and preparing for heat bursts is recognizing the events that come before heat bursts occur. Rain from a high convection cloud, falls below cloud level, and evaporates, cooling the air. Air parcels fall, which is cooler than the environment. And lastly, temperature conversion mixed with a downdraft momentum , continues downward until the air reaches the ground. The air parcels become warmer than its environment. McPherson, Lane, Crawford, and McPherson Jr. researched the heat burst system at the Oklahoma Mesonet, which is owned by both the University of Oklahoma and Oklahoma State University. The purpose of their research was to discover any technological benefits and challenges in detecting heat bursts, document the time of day and year that heat bursts mostly occur, and to research the topography of where heat bursts mostly occur in Oklahoma. Scientists and meteorologists use archived data to manually study data that detected 390 potential heat burst days during a fifteen year period. In studying the archived data, they observed that 58% of the potential days had dry-line passages, frontal passages or a temperature change. The temperature change was due to increase in solar radiation in the hours of the morning or a daytime precipitation weather system. By studying the archived data, the scientists' have the ability to determine the beginning, peak and end of heat burst conditions. The peak of heat burst conditions is the maximum observed temperature. The beginning of the heat burst occurrence is the time when the air temperature began to increase without decreasing until after the heat burst. The end of the heat burst is when the system ceased to affect the temperature and dew point of the area. In addition to researching the life cycle and characteristics of heat bursts, a group of scientists concluded that the topography of Oklahoma coincided with the change in atmospheric moisture between northwest and southeast Oklahoma. An increase in convection normally occurs over the United States High Plains during the late spring and summer. They also concluded that a higher increase in convection develops if a mid-tropospheric lifting mechanism interacts with an elevated moist layer.