A heat burst is a localized, short-lived meteorological event defined by a sudden and dramatic increase in surface air temperature, often accompanied by strong, dry, gusty winds. This phenomenon is typically associated with the collapse of a dying thunderstorm, often occurring in the late evening or overnight hours when the surrounding air is normally cooling. The rapid spike in heat can be extreme, leading to surface temperature rises of 10 to 20 degrees Fahrenheit or more within minutes.
The Adiabatic Mechanism of Formation
The mechanism behind a heat burst is rooted in the physics of a rapidly sinking column of air within a dissipating thunderstorm. This process begins when a thunderstorm, often in its decaying stage, loses the powerful updraft that once sustained it. A parcel of air high in the atmosphere starts to descend toward the surface as a downdraft.
As this air descends, it encounters residual precipitation, like rain or hail, that is evaporating into the very dry air layer present at mid-levels of the atmosphere. This evaporation, which is a cooling process, initially makes the air parcel denser and accelerates its downward motion. The precipitation, however, completely evaporates before the air reaches the ground, leaving a column of descending, dry air.
The air parcel then undergoes a physical process known as adiabatic compression as it continues its swift descent. The increasing atmospheric pressure at lower altitudes compresses the air, and this compression directly translates into a significant rise in the air’s temperature.
This warming occurs at a rate close to the dry adiabatic lapse rate, which is approximately 9.8 degrees Celsius for every kilometer the air descends. The surface experiences the heat burst when this exceptionally warm, compressed air finally reaches the ground.
Key Meteorological Signatures
The arrival of the compressed air parcel at the surface results in a set of distinct meteorological signatures. The most dramatic effect is the sudden, sharp rise in surface temperature, which can happen in a matter of minutes. For instance, one recorded event in Wichita, Kansas, saw the temperature jump from 85 degrees Fahrenheit to 102 degrees Fahrenheit in just 20 minutes.
Simultaneously, the heat burst is characterized by an extreme decrease in relative humidity, as the descending air is exceptionally dry. The dew point can drop substantially, sometimes by 15 to 30 degrees Fahrenheit. The event is also accompanied by strong, gusty winds that can sometimes reach damaging speeds, occasionally exceeding 70 or 80 miles per hour.
These signatures are localized and short-lived, typically lasting only for a few minutes to an hour. The high temperatures, combined with the low humidity and strong winds, can quickly desiccate vegetation in the affected area. The combination of these rapid changes provides a clear distinction from other common weather events.
How Heat Bursts Differ from Downbursts and Heat Waves
Heat bursts, downbursts, and heat waves all involve high temperatures or strong winds, but they are fundamentally different atmospheric events. A downburst is a powerful, localized column of sinking air within a thunderstorm that produces an outward burst of damaging winds upon hitting the ground. While both involve a strong downdraft, a typical downburst causes a sudden drop in temperature at the surface due to the presence of rain-cooled air.
The distinguishing factor for a heat burst is the intense warming caused by adiabatic compression, which occurs only after all precipitation has evaporated in a dry air environment. The effect on surface temperature is opposite: a downburst cools the air, while a heat burst dramatically heats it. A heat burst is considered a rare, dry variation of a downburst.
A heat burst is also easily distinguished from a heat wave, which is a prolonged period of abnormally high temperatures and often high humidity affecting a broad region. Heat waves develop over days and last for days or weeks, representing a large-scale meteorological pattern. Conversely, a heat burst is a sudden, localized, and short-duration weather event, lasting just minutes, that is tied directly to the collapse of a single storm system.