WunderBlog Archive » Weather Extremes
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Heat Bursts
A rare and intense heat burst affected south-central Nebraska early Tuesday morning rising the temperature from 73°F at 2 a.m. to 97°F by 4 a.m. in Hastings. Herein is a summary of the event and other notable heat bursts that have occurred in the past.
Between 1 a.m. and 4 a.m. CST on June 11th dissipating thunderstorms in the Grand Island, Nebraska area created conditions conducive to the development of heat bursts. At Grand Island the temperature rose from 73° (2:53 a.m.) to 90° (3:37 a.m.) and at Kearny from 75° (12:55 a.m.) to 97° (3:15 a.m.). Holdrege and Lexington also saw sharp temperature increases, but Hastings seems to have measured the most pronounced effects with its 24° rise from 73° to 97°. Here are the METARS and graphs for that site Tuesday morning:
METARS and observation graphs for Hastings on Tuesday June 11th. From wunderground.com
What Causes a Heat Burst?
The NWS office at Hastings published a statement Tuesday morning that included a very good explanation of what causes heat bursts to occur. I quote here:
A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air the precipitation begins evaporating thus causing the air to cool. As this air cools it will become more dense...eventually more dense compared to the surrounding warmer air and as a result begins descending to the surface at a high rate of speed. Eventually all of the precipitation within the descending air evaporates. At this point the air is completely dry and because no more evaporation can occur the air can no longer cool. The air, however, continues to descend towards the surface due to the momentum it has already acquired. As dry air descends through the atmosphere compression due to increasing atmospheric pressure causes the air to warm. It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air so the dry air continues to descend all the while warming more and more due to the aforementioned compressional heating. Eventually this descending air reaches the surface and the momentum (which was moving downward towards the surface) is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry air mass from aloft will cause the temperature at the surface to increase very quickly and the dew point at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of such rare.
A graphic of how a heat burst occurs.
This photograph illustrates a line of dissipating thundershowers with their attendant virga. It is a situation such as this which is the most common cause of a heat burst which, in fact, did occur with this line of showers in Texas on May 28, 2007. Photo from West Texas Mesonet which has a very informative blog on heat bursts in Texas in 2007.
Heat Bursts Around the World
Some extreme examples of heat bursts reported from around the world include temperature reports of 152° at Antalya, Turkey, on July 10, 1977; a temperature rise from 100° to 158° in two minutes near Lisbon, Portugal, on July 6, 1949; and an unbelievable 188° shade temperature apparently recorded in June 1967, at Abadan, Iran, where press reports said dozens of people died and asphalt streets liquefied. These reports from Portugal, Turkey, and Iran are almost certainly apocryphal; there appears to be no corroborating information aside from the original press reports themselves and investigation of weather observations from the areas at the purported time of occurrence show no evidence to support these extreme reports.
A verified heat burst at Kimberley, South Africa, raised the temperature from 67° to 110° in five minutes between 9:00 p.m. and 9:05 p.m. during a thunderstorm squall. The local weather observer stated that he believed the temperature actually rose higher than 110°, but his thermometer was not quick enough to register the highest point. The temperature had fallen back down to 67° by 9:45 p.m.
Heat Bursts in North America
GEORGIA
In 1860, Scientific American (vol.3:106) gave the following report of two heat flashes (no dates of occurrence were given):
"A hot wind extending about 100 yards in width, lately passed through middle Georgia, and scorched up the cotton crops on a number of plantations. A hot wind also passed through a section of Kansas; it burned up the vegetation in its track and several persons fell victim to its poisonous blast. It lasted for a very short period, during which the thermometer stood at 120° F".
MINNESOTA
The Minneapolis Tribune published the following story on July 10, 1879: "A blast of hot air passed from south to north through portions of New Ulm and Renville County last Sunday evening. It lasted only a minute or two, but so intense was the heat that people rushed out of their houses believing them to be on fire".
OKLAHOMA
A heat flash raised the temperature to 136° south of Cherokee, Oklahoma, at 3 a.m. on July 11, 1909. Crops in a small area at the center of the heat burst are said to have been instantly desiccated.
A heat burst at Gage on July 7, 1993, raised the temperature from 85° at 10:54 p.m. to 102° at midnight.
On the night of May 22, 1996, a heat burst emanating from collapsing thunderstorms near Ninnekah raised the temperature from the low 80°s to 105° between 11 p.m. and 3 a.m.
TEXAS
Just after midnight on the morning of June 15, 1960, a blast of hot wind estimated at 80–100 mph drove the temperature from 70° up to 140° on the northwest side of Lake Whitney, northwest of Waco. Cotton fields were reported to have been carbonized, leaving only burnt stalks standing.
MANITOBA, CANADA
Gretna, Manitoba experienced two heat bursts during the night of July 20–21, 1960, when the temperature rose from 80° to 96° for 15 minutes between 12:25 and 12:40 a.m. It fell back to a much lower temperature and then rose again to 97° for 15 minutes between 2:00 a.m. and 2:15 a.m.
SOUTH DAKOTA
Temperature rose from 85° at 1 a.m. to 104° at 3 a.m. in Pierre, South Dakota, the morning of June 20, 1989. Sioux Falls saw its temperature spike from 73° to 101° in 10 minutes the morning of August 3, 2008.
Thermograph for Sioux Falls during the August 3, 2008 heat burst event. The trace could not quite keep up with the actual rapid heating, hence the difference between the measured high of 101° and the trace high of 99°.
MONTANA
Great Falls reported a temperature rise from 67° to 93° in 15 minutes between 5:02 and 5:17 a.m. on September 9, 1994, tying the record high temperature for the date. The temperature then fell back to 68° by 5:40 a.m.
Question
Should temperatures measured during heat burst events be considered 'official' measurements in so far as 'all time' record heat observations?
Christopher C. Burt
Weather Historian
A rare and intense heat burst affected south-central Nebraska early Tuesday morning rising the temperature from 73°F at 2 a.m. to 97°F by 4 a.m. in Hastings. Herein is a summary of the event and other notable heat bursts that have occurred in the past.
Between 1 a.m. and 4 a.m. CST on June 11th dissipating thunderstorms in the Grand Island, Nebraska area created conditions conducive to the development of heat bursts. At Grand Island the temperature rose from 73° (2:53 a.m.) to 90° (3:37 a.m.) and at Kearny from 75° (12:55 a.m.) to 97° (3:15 a.m.). Holdrege and Lexington also saw sharp temperature increases, but Hastings seems to have measured the most pronounced effects with its 24° rise from 73° to 97°. Here are the METARS and graphs for that site Tuesday morning:
METARS and observation graphs for Hastings on Tuesday June 11th. From wunderground.com
What Causes a Heat Burst?
The NWS office at Hastings published a statement Tuesday morning that included a very good explanation of what causes heat bursts to occur. I quote here:
A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air the precipitation begins evaporating thus causing the air to cool. As this air cools it will become more dense...eventually more dense compared to the surrounding warmer air and as a result begins descending to the surface at a high rate of speed. Eventually all of the precipitation within the descending air evaporates. At this point the air is completely dry and because no more evaporation can occur the air can no longer cool. The air, however, continues to descend towards the surface due to the momentum it has already acquired. As dry air descends through the atmosphere compression due to increasing atmospheric pressure causes the air to warm. It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air so the dry air continues to descend all the while warming more and more due to the aforementioned compressional heating. Eventually this descending air reaches the surface and the momentum (which was moving downward towards the surface) is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry air mass from aloft will cause the temperature at the surface to increase very quickly and the dew point at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of such rare.
A graphic of how a heat burst occurs.
This photograph illustrates a line of dissipating thundershowers with their attendant virga. It is a situation such as this which is the most common cause of a heat burst which, in fact, did occur with this line of showers in Texas on May 28, 2007. Photo from West Texas Mesonet which has a very informative blog on heat bursts in Texas in 2007.
Heat Bursts Around the World
Some extreme examples of heat bursts reported from around the world include temperature reports of 152° at Antalya, Turkey, on July 10, 1977; a temperature rise from 100° to 158° in two minutes near Lisbon, Portugal, on July 6, 1949; and an unbelievable 188° shade temperature apparently recorded in June 1967, at Abadan, Iran, where press reports said dozens of people died and asphalt streets liquefied. These reports from Portugal, Turkey, and Iran are almost certainly apocryphal; there appears to be no corroborating information aside from the original press reports themselves and investigation of weather observations from the areas at the purported time of occurrence show no evidence to support these extreme reports.
A verified heat burst at Kimberley, South Africa, raised the temperature from 67° to 110° in five minutes between 9:00 p.m. and 9:05 p.m. during a thunderstorm squall. The local weather observer stated that he believed the temperature actually rose higher than 110°, but his thermometer was not quick enough to register the highest point. The temperature had fallen back down to 67° by 9:45 p.m.
Heat Bursts in North America
GEORGIA
In 1860, Scientific American (vol.3:106) gave the following report of two heat flashes (no dates of occurrence were given):
"A hot wind extending about 100 yards in width, lately passed through middle Georgia, and scorched up the cotton crops on a number of plantations. A hot wind also passed through a section of Kansas; it burned up the vegetation in its track and several persons fell victim to its poisonous blast. It lasted for a very short period, during which the thermometer stood at 120° F".
MINNESOTA
The Minneapolis Tribune published the following story on July 10, 1879: "A blast of hot air passed from south to north through portions of New Ulm and Renville County last Sunday evening. It lasted only a minute or two, but so intense was the heat that people rushed out of their houses believing them to be on fire".
OKLAHOMA
A heat flash raised the temperature to 136° south of Cherokee, Oklahoma, at 3 a.m. on July 11, 1909. Crops in a small area at the center of the heat burst are said to have been instantly desiccated.
A heat burst at Gage on July 7, 1993, raised the temperature from 85° at 10:54 p.m. to 102° at midnight.
On the night of May 22, 1996, a heat burst emanating from collapsing thunderstorms near Ninnekah raised the temperature from the low 80°s to 105° between 11 p.m. and 3 a.m.
TEXAS
Just after midnight on the morning of June 15, 1960, a blast of hot wind estimated at 80–100 mph drove the temperature from 70° up to 140° on the northwest side of Lake Whitney, northwest of Waco. Cotton fields were reported to have been carbonized, leaving only burnt stalks standing.
MANITOBA, CANADA
Gretna, Manitoba experienced two heat bursts during the night of July 20–21, 1960, when the temperature rose from 80° to 96° for 15 minutes between 12:25 and 12:40 a.m. It fell back to a much lower temperature and then rose again to 97° for 15 minutes between 2:00 a.m. and 2:15 a.m.
SOUTH DAKOTA
Temperature rose from 85° at 1 a.m. to 104° at 3 a.m. in Pierre, South Dakota, the morning of June 20, 1989. Sioux Falls saw its temperature spike from 73° to 101° in 10 minutes the morning of August 3, 2008.
Thermograph for Sioux Falls during the August 3, 2008 heat burst event. The trace could not quite keep up with the actual rapid heating, hence the difference between the measured high of 101° and the trace high of 99°.
MONTANA
Great Falls reported a temperature rise from 67° to 93° in 15 minutes between 5:02 and 5:17 a.m. on September 9, 1994, tying the record high temperature for the date. The temperature then fell back to 68° by 5:40 a.m.
Question
Should temperatures measured during heat burst events be considered 'official' measurements in so far as 'all time' record heat observations?
Christopher C. Burt
Weather Historian
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.