Author Topic: Heat Bursts? Why only at night?  (Read 13027 times)

electrobleme

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Heat Bursts? Why only at night?
« on: October 07, 2009, 05:37:09 »

Heat Bursts occur at night

Strange and puzzling Heat Bursts, are they caused by Thunderstorms or a secondary effect of what caused the Thunderstorm?


electrobleme

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Heat Bursts - what are they - scientific answer
« Reply #1 on: October 07, 2009, 05:39:31 »


Heat Bursts

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Heat Bursts

Dry heatbursts are responsible for a rare weather event called "Heat Bursts". Heat bursts usually occur at night, are associated with decaying thunderstorms, and are marked by gusty, sometimes damaging, winds, a sharp increase in temperature and a sharp decrease in dewpoint.

While not fully understood, it is thought that the process of creating a dry microburst begins higher in the atmosphere for heat bursts. A pocket of cool air aloft forms during the evaporation process since heat energy is required. In heat bursts, all the precipitation has evaporated and this cooled air, being more dense than the surrounding environment, begins to sink due to gravity.

As the air sinks it compresses and with no more water to evaporate the result is the air rapidly warms. In fact, it can become quite hot and very dry. Temperatures generally rise 10 to 20 degrees in a few minutes and have been known to rise to over 120°F (49°C) and remain in place for several hours before returning to normal.
Heat Bursts - oceanservice.noaa .gov

electrobleme

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Heat burst captured by weather network in Oklahoma
« Reply #2 on: October 07, 2009, 05:44:00 »
Heat burst captured by weather network in Oklahoma

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Heat burst captured by weather network

High winds and a temperature jump from what meteorologists call a "heat burst" hit 10 Oklahoma counties the evening of May 22-23, toppling trees, ripping down power lines and lifting roofs off homes and businesses. The temperature in Chickasha, just southwest of Oklahoma City, jumped from 88 to 102 degrees between 9:00 and 9:25 p.m. A network of automated weather observing stations sprinkled across Oklahoma captured details of the heat burst for study.

A total of 111 sites make up the Oklahoma Mesonetwork with as many as four in each of the state's counties. This dense network of surface observing stations collects weather information such as temperature, humidity, surface air pressure, wind speed and direction, soil temperature and incoming solar radiation. This data benefits agriculture. It's also vital to forecasters when severe thunderstorms are possible. The Mesonet, as it's called, detected the heat burst in its early stages, allowing the National Weather Service to issue high wind warnings for southwest and central Oklahoma counties blasted by the hot, dry wind.

Any tall, dying storm can produce a heat burst if enough evaporation takes place above the ground. They are relatively unusual, but no one knows how many occur because many are probably never detected by weather instruments. The heat burst that hit Oklahoma was unusually strong.

The table below shows Chickasha and Ninnekah Mesonet data taken every five minutes during the heat burst. The two sites are near each other so the data is similar. Temperature is given in degrees Fahrenheit and wind speed is a five-minute average. In addition, wind gusts reached 105 mph in Tipton, 95 mph in Lawton, 67 mph in Ninnekah and 63 mph in Chickasha the evening of May 22. Eventually friction from the earth's surface slowed the wind to a stiff breeze but this took much of the night.

                   Chickasha           Ninnekah
Time (p.m.) Temp.  Wind Speed   Temp.  Wind Speed
 9:00      87.6                 25.5      87.9      19.4
 9:05      88.1                 31.5      88.8      30.1
 9:10      88.6                 30.8      91.6      26.4
 9:15      89.8                10.5      95.8      26.0
 9:20      96.4                25.2      98.5      23.5
 9:25     101.9                20.6      98.6      25.0
 9:30      99.1               21.2      99.8      28.2
 9:35      98.0              24.3     100.9      29.9
 9:40      98.7               31.1     101.4      37.6
 9:45      97.7               44.2      98.4      43.1
 9:50      97.6               46.1      97.4      40.4
 9:55      97.6              42.7      96.6      36.5
10:00      96.9              43.5      95.0      44.7
10:05      95.8             43.6      92.1      41.6
10:10      92.3             45.7      92.3      42.9
10:15      92.5              44.8      93.0      41.4

Source: The Oklahoma Mesonetwork

Heat burst captured by weather network - usatoday .com

Why does the wind get faster after the peak in temperature when the temp starts to go down?

« Last Edit: October 07, 2009, 05:47:48 by electrobleme »

electrobleme

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Late Night Heat Burst on the Lower Eastern Shore, April 25-26, 2009
« Reply #3 on: October 07, 2009, 06:01:32 »





Quote
Late Night Heat Burst on the Lower Eastern Shore, April 25-26, 2009

In the early morning hours of April 26, 2009, dying thunderstorms and a very warm, dry lower and middle atmosphere led to the occurrence of heat bursts over sections of the Maryland Lower Eastern Shore. They were localized in a relatively small area from Dorchester County, southeast into northern Accomack county, Virginia and Worchester County, Maryland. Evidence of the bursts were detected by weather observing equipment at Cambridge, Salisbury, Wallops Island and Ocean City (noted in the table below).

A heat burst is defined as localized, sudden increase in surface temperature associated with a thunderstorm, shower, or mesoscale convective system, often accompanied by extreme drying1. The most dramtic heat bursts can also cause severe wind gusts, which can occasionally result in property damage. However, it should be noted that no damage was reported in this case, with the highest heat burst induced wind gust of 52 MPH reported by the Automated Surface Observation System (ASOS) at the Salisbury Airport.

Heat bursts usually occur in the late evening and early morning hours, and occur generally in the late spring and summer. The two primary reasons for this are the onset of the nighttime inversion and thunderstorm climatology. Heat bursts are not very common across our area, and are more often found across the Plains states.

Specific information on the heat bursts detected at each affected observing station are found below. The increase in temperature and decrease in dewpoint during this period as a result of the bursts are denoted below. The departure from the minimum temperature/maximum dewpoint BEFORE the heat burst is noted in parentheses to the right of the maximum temperature and minimum recorded dew point.


Late Night Heat Burst on the Lower Eastern Shore, April 25-26, 2009 - erh.noaa .gov

The website has a lot more information, radar shots and information on this heat burts.


electrobleme

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Late Night Heat Burst in Western Minnesota on July 16-17, 2006
« Reply #4 on: October 07, 2009, 06:14:17 »
Late Night Heat Burst in Western Minnesota on July 16-17, 2006


Quote
....A heat burst is characterized by a dramatic, almost instantaneous, rise in temperature and fall in dew point temperature. Most, but not all, heat bursts are also accompanied by a drop in surface pressure, little to no precipitation, and gusty, rapidly shifting winds.....

Heat bursts are typically a late spring and summer, as well as a late evening and nighttime, phenomenon. The two primary reasons for this are the onset of the nighttime inversion and thunderstorm climatology. Most heat bursts are also detected in the Plains states, but heat bursts have also been recorded overseas, including the United Kingdom and Yemen.....

Late Night Heat Burst in Western Minnesota on July 16-17, 2006 - crh.noaa.gov

The sudden drop in the Dew Point before the temperature rises is very interesting. Why the sudden loss of water in the atmosphere? Less water mean a lot less conductivity of electricity and then the air temperature starts to rapidly rise.

Also the drop in air pressure is very significant, less electrical conductivity means less air pressure?


« Last Edit: October 07, 2009, 06:16:53 by electrobleme »

electrobleme

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Examination of a long-lived heat burst event in the northern plains
« Reply #5 on: October 07, 2009, 06:26:23 »

Examination of a long-lived heat burst event in the northern plains

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Examination of a long-lived heat burst event in the northern plains

Several heat bursts were observed across portions of northern Nebraska and southern South Dakota during the local morning hours of 30 July 2001.

These heat bursts were noted by a marked increase in temperatures, decrease in dewpoint temperatures, pressure falls, and gusty surface winds.

Due to the sparsity of surface observations in this region, only a few reports of this phenomenon were confirmed; however, the data that were collected indicate this event was unusual in that it persisted for over seven hours with a horizontal extent of at least 230 nm.
Few events of this magnitude have been documented. It is significant to note that damaging surface winds were also recorded with this event, something rarely documented in association with heat bursts.
Examination of a long-lived heat burst event in the northern plains - findarticles .com

This heat burst lasted for over 7 hours!

The full article can be read here