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Sudden increase in atmospheric temperature
In meteorology, a heat burst is a rare atmospheric phenomenon characterized by a sudden, localized increase in air temperature near the Earth's surface. Heat bursts typically occur during night-time and are associated with decaying thunderstorms. They are also characterized by extremely dry air and are sometimes associated with very strong, even damaging, winds.
Although the phenomenon is not fully understood, the event is thought to occur 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 40 °C (104 °F), sometimes rising by 10 °C (18 °F) or more within only a few minutes. More extreme events have also been documented, where temperatures have been reported to exceed 50 °C (122 °F). However, such extreme events have never been officially verified.
In general, heat bursts occur during the late spring and summer seasons. During these times, air-mass thunderstorms tend to generate due to daytime heating and lose their main energy during the evening hours. Due to the potential temperature increase, heat bursts normally occur at night, though they have also been recorded during the daytime. Heat bursts can vary widely in duration, from a couple of minutes to several hours. The phenomenon is usually accompanied by strong gusty winds, extreme temperature changes, and an extreme decrease in humidity. They may occur near the end of a weakening thunderstorm cluster. Dry air and a low-level temperature inversion may also be present during the storm.
Heat bursts are thought to be caused by a mechanism similar to that of downbursts. As the thunderstorm starts to dissipate, the layer of clouds starts to rise. After the clouds have risen, 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 updraft-related fuel. The raindrops begin to evaporate into dry air, which reinforces the effects of the heat burst (evaporation cools the air, increasing its density). As the unsaturated air descends into lower levels of the atmosphere, the air pressure increases. The descending air parcel warms at the dry adiabatic lapse rate of approximately 10 °C per 1000 meters (5.5 °F 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 weakened, containing light rain showers and snow showers. It was followed by gusty winds and a temperature increase. The detection proved that heat bursts can occur in both summer months and winter months, and also that a weakening thunderstorm was not necessary for the development of a heat burst.
The first step in forecasting and preparing for heat bursts is recognizing the events that precede them. Rain from a high convection cloud falls below cloud level and evaporates, cooling the air. Air parcels that are cooler than the surrounding environment descend in altitude. Lastly, temperature conversion mixed with a downdraft momentum continues downward until the air reaches the ground. The air parcels then become warmer than their 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, to document the time of day and year at which heat bursts are most likely to occur, and to research the topography of where heat bursts are most likely to 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 due to an increase in solar radiation in the hours of the morning or a daytime precipitation weather system.
By studying the archived data, 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 a heat burst is the time during which the air temperature increases without decreasing until after the peak; the end of a heat burst is when the system ceases 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 High Plains of the United States 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.
Friona, Texas, 13 June 2021: From 1:25 am to 2:00 am CDT, the temperature rose 18 degrees from 70 °F (21 °C) to 88.1 °F (31.2 °C), along with a 68 miles per hour (109 km/h) damaging wind gust.
Edmond, Oklahoma, 4 June 2020: At 10:17 PM, the temperature dramatically rose to 97 °F (36 °C), with surrounding readings being in and around 80 °F (27 °C).
Chicago, Illinois, 16 July 2017: Two heat bursts occurred from decaying thunderstorms at both Chicago O'Hare and Chicago Midway airports. From 3:05 am to 3:30 am, O'Hare rose from 72 °F (22 °C) to 79 °F (26 °C), and from 3:45 am to 3:55 am, Midway rose from 73 °F (23 °C) to 81 °F (27 °C).
Hobart, Oklahoma, 6-7 July 2016: The temperature rose from 80.6 °F (27.0 °C) just before 11:00 PM CDT, 6 July, to 105.8 °F (41.0 °C) at 12:15 AM CDT, 7 July.
Calgary, Alberta, 29-31 July 2014: Between 10:00 PM on 29 July and 12:00 AM on 30 July, the dew point fell from 12 °C (54 °F) to 0 °C (32 °F), with southwest wind gusts of 85 kilometres per hour (53 mph) at the airport. Meanwhile, the mercury rose from 26 °C (79 °F) to 29 °C (84 °F). On 31 July 2014, a second heat burst began about 9:30 PM, with the wind gusting to 67 kilometres per hour (42 mph), the dew point falling from 10 °C (50 °F) to 0 °C (32 °F), and the temperature climbing from 26 °C (79 °F) to 29 °C (84 °F).
Melbourne, Victoria, 14-15 January 2014: Following a very hot day, decaying thunderstorms produced a heat burst centered over the western suburbs of the city, but affecting most of the urban area. At 10:50 PM, Laverton recorded a wind gust of 102 km/h (55 kn; 63 mph), followed by a rise in temperature from 29.9 to 38.9 °C (85.8 to 102.0 °F) in just over an hour, while Cerberus station recorded a rise from 24.2 to 32.5 °C (75.6 to 90.5 °F) in 30 minutes and later recorded a second rise from 26.6 to 33.6 °C (79.9 to 92.5 °F) in 46 minutes. The main Melbourne weather station recorded a smaller rise from 33.6 to 36.4 °C (92.5 to 97.5 °F) in 90 minutes.
Grand Island, Nebraska, 11 June 2013: Temperature jumped from 74.2 °F (23.4 °C) to 93.7 °F (34.3 °C) in the 15 minutes between 2:57 and 3:12 AM.
Dane County, Wisconsin, 15 May 2013: The National Weather Service reported nearly a 10 °F (5.3 °C) temperature boost that coincided with sustained winds.
South Dakota, 14 May 2013: Between 7:00 AM CDT and 8:00 AM CDT, several "heat bursts" or hybrid "heat burst/wake low"-induced wind gusts were observed across portions of northeastern South Dakota, during which temperatures rose from 58 °F (14 °C) to 79 °F (26 °C) and strong winds up to 57 miles per hour (92 km/h) were reported.
Georgetown, South Carolina, 1 July 2012: Between 9:00 PM and 10:30 PM, the temperature rose from 79 °F (26 °C) to 90 °F (32 °C) and the dew point fell from 59 °F (15 °C) to 45 °F (7 °C).
Bussey, Iowa, 3 May 2012: The temperatures shot from about 74 °F (23 °C) to about 85 °F (29 °C) degrees while peak wind gusts jumped from around 15 mph to about 60 mph.
Torcy, Seine-et-Marne, France, 29 April 2012: While an area of low pressure moved from the southwest of France to the northwest, the wind suddenly increased between 10 PM and midnight in areas to the south of Paris. Sustained winds topped 45 kilometres per hour (28 mph) at the station of Torcy (Seine-et-Marne) with gusts of up to 110 kilometres per hour (68 mph). At the same time, the temperature rose from 13.4 °C (56.1 °F) at 11 PM to 24 °C (75 °F) at midnight. The vertical temperature profile was similar to that observed during dry downbursts, with a very strong helicity (700 m2/s²) and a strong shear (60 kn) but with only a weak instability (CAPE levels of 100 to 200 J/kg). No thunderstorms developed over the region, however light rain was reported (due to evaporation in the dry low-level boundary layer). Other stations in the area also experienced the phenomenon but not as dramatically as in Torcy.
Atlantic, Iowa, 23 August 2011: The observation at the Atlantic AWOS at 7:25 PM local time had a temperature of 102 °F (39 °C) and a dew point of 7 °F (-14 °C). Three observations prior to this (6:55 PM), the temperature was 88 °F (31 °C) and the dew point was 64 °F (18 °C). The 7 °F (-14 °C) dew point is considered likely to be incorrect, however, as AWOS stations have been known to have issues with dew points in low-humidity environments. Scattered wind damage was also reported in association with the heat bursts, with one wind observation as high as 60 mph (97 km/h).
Indianapolis, Indiana, 3 July 2011: Observations around 1:30 AM EDT in the area indicated the temperature rose and the dew point dropped nearly 15 °F (8.3 °C) in less than an hour, causing the relative humidity to drop nearly 40-50 percentage points. Winds increased rapidly, with gusts to near 50 mph (80 km/h). One NWS Indianapolis employee reported that his neighbor's patio furniture ended up in his backyard. The observation site at Eagle Creek Airpark (KEYE) best observed the temperature, dew point, and pressure changes. The site at Indianapolis International Airport (KIND) observed the strongest wind gusts associated with the heat burst.
Wichita, Kansas, 9 June 2011: Temperatures rose from 85 to 102 °F (29 to 39 °C) between 12:22 and 12:42 AM. The heat burst caused some wind damage (40-50 mph or 64-80 km/h) and local residents reported the phenomenon to area weather stations.
Buenos Aires, Argentina, 29 October 2009: After a day with extremely high and unusual temperatures that peaked over 93.9 °F (34.4 °C) (air temperature 101.6 °F (38.7 °C)), at late midnight temperatures rose from 87.8 to 94.2 °F (31.0 to 34.6 °C) in a matter of minutes, with wind gusts over 37 miles per hour (60 km/h).
Edmonton, Alberta, 18 August 2008: In the evening temperatures were cooling off after a high of 34.4 °C (93.9 °F). Thunderstorms had formed to the southwest along the foothills, and were moving to the east-northeast. By 22:37 PM MST, the temperature at the Edmonton City Centre Airport was 22 °C (72 °F), with the dew point at 16 °C (61 °F) and light rain from the thunderstorm passing the city. Around 23:00, strong gusts of wind from 37 to 57 kilometres per hour (23 to 35 mph) were recorded at the airport. The temperatures quickly rose to 31 °C (88 °F) and lowered the dew point to 10 °C (50 °F), lasting less than an hour. The burst was caused by the thunderstorms dissipating to the north and east of the city.
Sioux Falls, South Dakota, 3 August 2008: Temperatures rose rapidly from the lower 70 to 101 °F (21 to 38 °C) in a matter of minutes. Wind speeds also rose with gusts up to 50-60 mph (80-97 km/h).
Cozad, Nebraska, 26 June 2008: Wind gusts reached 75 miles per hour (121 km/h), as the temperature rose 20 °F (11 °C) in a matter of minutes.
Midland, Texas, 16 June 2008: At 11:25 PM, a wind gust of 62 mph (100 km/h) occurred, and the temperature rose from 71 to 97 °F (21.7 to 36.1 °C) in minutes. (These measurements were taken from miles away, and theories point to 80-100 mph (130-160 km/h) winds in a 2–3-block perimeter.)
Emporia, Kansas, 25 May 2008: Reported temperature jumped from 71 to 91 °F (21.7 to 32.8 °C) between 4:44 and 5:11 AM CDT as the result of wind activity from a slow-moving thunderstorm some 40 miles (64 km) to the southwest.
Canby, Minnesota, 16 July 2006: A heat burst formed in Western Minnesota, pushing Canby's temperature to 100 °F (37.8 °C) and causing a wind gust of 63 mph (55 kn; 101 km/h). The dew point fell from 70 to 32 °F (21 to 0 °C) over the course of one hour.
Hastings, Nebraska, 20 June 2006: During the early morning the surface temperature abruptly increased from approximately 75 to 94 °F (23.9 to 34.4 °C).
Oklahoma, 22–23 May 1996: The temperature in the towns of Chickasha rose from 87.6 to 101.9 °F (30.9 to 38.8 °C) in just 25 minutes, while the temperature at Ninnekah rose from 87.9 to 101.4 °F (31 to 39 °C) in 40 minutes. In addition, wind damage was reported as winds gusted to 95 mph (153 km/h) in Lawton, 67 mph (108 km/h) in Ninnekah, and 63 mph (101 km/h) in Chickasha.
Barcelona, Spain, 4-5 August 1993 and 2 July 1994: Heat bursts with temperature increases exceeding 13 °C (23 °F) and wind gusts of more than 44 knots (51 mph) were recorded at Barcelona-El Prat Airport, a record maximum temperature at the airport, and caused the spread of forest fires.
^National Weather Service. Wilmington, North Carolina. "Georgetown Heat Burst." Retrieved from www.weather.gov/ilm/GeorgetownHeatBurst.
^Kenneth Crawford, Justin Lane, Renee McPherson, William McPherson Jr. "A Climatological Analysis of Heat Bursts in Oklahoma (1994-2009)." International Journal of Climatology. Volume 31. Issue 4. Pages 531-544. (10 Mar.).