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{{redirect|Electrical storm}}

[[Image:Rolling-thunder-cloud.jpg|thumb|right|399px|A [[shelf cloud]] associated with a heavy or severe thunderstorm over [[Enschede]], [[The Netherlands]].]]
{{Wiktionarypar|thunderstorm}}
A '''thunderstorm''', also known as an '''electrical [[storm]]''' or a '''lightning storm''', is a form of weather characterized by the presence of [[lightning]] and its effect: [[thunder]].<ref>{{cite web | date = [[21 April]] [[2005]] | url = http://www.weather.gov/glossary/index.php?letter=t | title = Weather Glossary - T | publisher = National Weather Service | accessdate = 2006-08-23}}</ref> It is usually accompanied by [[heavy rain (meteorology)|heavy rain]] and sometimes [[Thundersnow|snow]], [[hail]], or [[Dry thunderstorm|no precipitation]] at all. Thunderstorms may [[storm train|line up in a series]], and strong or severe thunderstorms may [[rotating thunderstorm|rotate]].
==Life cycle==
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<div style="border: none; width:500px;"><div class="thumbcaption"><center>''Airflow diagrams showing three stages of a thunderstorm life cycle.''</center></div></div></div>Warm air has a lower density than cool air, so warm air rises within cooler air, similar to [[hot air balloon]]s. Clouds form as warm air carrying moisture rises within cooler air. As the warm air rises, it cools. The moist [[water vapor]] begins to [[condensation|condense]]. When the moisture condenses, this releases energy that keeps the air warmer than its surroundings, so that it continues to rise. If enough [[Convective available potential energy|instability]] is present in the atmosphere, this process will continue long enough for [[Cumulonimbus|cumulonimbus clouds]] to form, which support lightning and thunder.

All thunderstorms, regardless of type, go through three stages: the '''cumulus stage''', the '''mature stage''', and the '''dissipation stage'''. Depending on the conditions present in the atmosphere, these three stages can take anywhere from 20 minutes to several hours to occur.

===Cumulus stage===
The first stage of a thunderstorm is the cumulus stage, or developing stage. In this stage, masses of moisture are lifted upwards into the atmosphere. The trigger for this lift can be [[insolation]] heating the ground producing [[thermals]], areas where two winds converge forcing air upwards, or where winds blow over terrain of increasing elevation. The moisture rapidly cools into liquid drops of water, which appears as ''cumulus'' clouds. As the water vapor condenses into liquid, [[latent heat]] is released which warms the air, causing it to become less dense than the surrounding dry air. The air tends to rise in an ''updraft'' through the process of [[convection]] (hence the term [[Precipitation (meteorology)|convective precipitation]]). This creates a [[low pressure area|low-pressure zone]] beneath the forming thunderstorm. In a typical thunderstorm, approximately 5×10<sup>8</sup> [[kilograms|kg]] of water vapor are lifted, and the amount of [[energy]] released when this condenses is about equal to the energy used by a city ([[United States|US]]-2002) of 100,000 during a month.{{Fact|date=January 2008}}

===Mature stage===
[[Image:Anvil shaped cumulus panorama edit crop.jpg|thumb|right|Anvil shaped thundercloud in the mature stage over [[Swifts Creek, Victoria]]]][[Image:CloudOverUtah.jpg|thumb|right|Cumulonimbus cloud over [[White Canyon]] in Utah]]In the mature stage of a thunderstorm, the warmed air continues to rise until it reaches existing air which is warmer, and the air can rise no further. Often this 'cap' is the [[tropopause]]. The air is instead forced to spread out, giving the storm a characteristic anvil shape. The resulting cloud is called ''[[cumulonimbus incus]]''. The water droplets [[coalescence (meteorology)|coalesce]] into heavy droplets and freeze to become ice particles. As these fall they melt to become [[rain]]. If the updraft is strong enough, the droplets are held aloft long enough to be so large that they do not melt completely and fall as [[hail]]. While updrafts are still present, the falling rain creates ''downdrafts'' as well. The simultaneous presence of both an updraft and downdrafts marks the mature stage of the storm, and during this stage considerable internal [[turbulence]] can occur in the storm system, which sometimes manifests as strong winds, severe lightning, and even [[tornado]]es.

Typically, if there is little [[wind shear]], the storm will rapidly enter the dissipating stage and 'rain itself out', but if there is sufficient change in wind speed and/or direction the downdraft will be separated from the updraft, and the storm may become a [[supercell]], and the mature stage can sustain itself for several hours.

In certain cases however, even with little wind shear, if there is enough atmospheric support and instability in place for the thunderstorm to feed on, it may even maintain its mature stage a bit longer than most storms.

===Dissipating stage===
[[Image:DissipatingThunderstormKent.jpg|thumb|right|A dissipating thunderstorm over [[Kent]], [[United Kingdom]], showing a magnificent display of [[mammatus]]]]
In the dissipation stage, the thunderstorm is dominated by the downdraft. If atmospheric conditions do not support super cellular development, this stage occurs rather quickly, approximately 20-30 minutes into the life of the thunderstorm. The downdraft will push down out of the thunderstorm, hit the ground and spread out. The cool air carried to the ground by the downdraft cuts off the inflow of the thunderstorm, the updraft disappears and the thunderstorm will dissipate.

==Classification==
[[Image:Thunderstorm over Wagga Wagga.jpg|thumb|right|A single cell thunderstorm over [[Wagga Wagga]].]]There are four main types of thunderstorms: single cell, multicell, squall line (also called multicell line) and supercell. Which type forms depends on the instability and relative wind conditions at different layers of the atmosphere ("[[wind shear]]").

===Single cell===
This term technically applies to a single thunderstorm with one main updraft. Within a cluster of thunderstorms, the term "cell" refers to each separate principal updraft.

Thunderstorm cells can and do form in isolation to other cells. Such storms are rarely severe and are a result of local atmospheric instability; hence the term "air mass thunderstorm". These are the typical summer thunderstorm in many temperate locales. They also occur in the cool unstable air which often follows the passage of a [[weather fronts|cold front]] from the sea during winter.

While most single cell thunderstorms move, there are some unusual circumstances where they remain stationary. When this happens, catastrophic flooding is possible. In [[Rapid City, South Dakota]], in 1972, an unusual alignment of winds at various levels of the atmosphere combined to produce a continuous, stationary cell which dropped an enormous quantity of rain, resulting in devastating flash flooding <ref>[http://www.crh.noaa.gov/unr/?n=weather NWS Rapid City, SD - The Rapid City Flood of 1972 > Weather<!-- Bot generated title -->]</ref>. A similar event occurred in [[Boscastle]], England, on [[16 August]] [[2004]] <ref>[http://www.tintagelweb.co.uk/BoscastleFlood.htm Boscastle Flood 2004<!-- Bot generated title -->]</ref>.

===Multicell cluster===
Multicell storms form as clusters of storms but may then evolve into one or more [[squall line]]s. They often arise from convective updrafts in or near mountain ranges and linear weather boundaries, usually strong cold fronts or troughs of low pressure.

===Multicell lines===
Multicell line storms, commonly referred to as "[[squall line]]s", occur when multi cellular storms form in a line rather than clusters. They can be hundreds of miles long, move swiftly, and be preceded by a [[gust front]]. Heavy rain, hail, lightning, very strong winds and even isolated tornadoes can occur over a large area in a squall line.<ref>{{cite web | date = [[October 4]] [[1999]] | url = http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/svr/type/mline/chr.rxml | title = Components of Multicell Lines | work = Weather World 2010 Project | publisher = University of Illinois | accessdate = 2006-08-23}}</ref> [[Bow echo]]es can form within squall lines, bringing with them even higher winds.

An unusually powerful type of squall line called a [[derecho]] occurs when an intense squall line travels for several hundred miles, often leaving widespread damage over thousands of square miles.

Occasionally, squall lines also form near the outer rain band of tropical cyclones. The squall line is propelled by its own outflow, which reinforces continuous development of updrafts along the leading edge.

This kind of storm is also known as "Wind of the Stony Lake" (Traditional Chinese:石湖風, Simplified Chinese: 石湖风) in southern China.<ref>{{cite web | date = [[17 June]] [[2005]] | url = http://www.hko.gov.hk/education/edu01met/wxphe/ele_squalle.htm | title = Squall lines and "Shi Hu Feng" - what you want to know about the violent squalls hitting Hong Kong on [[9 May]] [[2005]] | publisher = Hong Kong Observatory | accessdate = 2006-08-23}}</ref>

{{See also|List of derecho events}}

===Supercell===
{{Main|Supercell}}
[[Image:Thunderhead.anvil.jpg|thumb|right|The setting sun illuminates the top of a classic anvil-shaped thunderstorm cloud in eastern [[Nebraska]], [[United States]].]]

[[Supercell]] storms are large, severe quasi-steady-state storms which feature wind speed and direction that vary with height ("wind shear"), separate downdrafts and updrafts (i.e., precipitation is not falling through the updraft) and a strong, rotating updraft (a "[[mesocyclone]]"). These storms normally have such powerful updrafts that the top of the cloud (or anvil) can break through the troposphere and reach into the lower levels of the stratosphere and can be {{convert|15|mi|km|0}} wide. These storms can produce destructive tornadoes, sometimes [[Fujita scale|F3]] or higher, extremely large hailstones (4 inch or 10 cm diameter), straight-line winds in excess of 80 mph (130 km/h), and [[flash flood]]s. In fact, most [[tornadoes]] occur from this type of thunderstorm.<ref>{{cite web |date =[[October 4]] [[1999]] |url=http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/svr/type/spr/home.rxml |title=Supercell Thunderstorms |work=Weather World 2010 Project |publisher=University of Illinois |accessdate=2006-08-23}}</ref>

===Severe thunderstorm===
{{Expand|section|date=July 2007}}

A severe thunderstorm is a term designating a thunderstorm that has reached a predetermined level of severity. Often, this level is determined by the storm being strong enough to inflict wind or hail damage. In the United States, a storm is considered severe if winds reach over 50&nbsp;knots (58&nbsp;mph or 93&nbsp;km/h), hail is ¾&nbsp;inch (2&nbsp;cm) diameter or larger, or if [[funnel cloud]]s and/or [[tornado]]es are reported.<ref>{{cite web | title =Weather Glossary - S | publisher =[[National Weather Service]] | date =[[2005-04-21]] | url =http://www.weather.gov/glossary/index.php?letter=s | accessdate =2007-06-17 }}</ref> Though a funnel cloud or tornado indicates the presence of a severe thunderstorm, a [[tornado warning]] would then be issued in place of a [[severe thunderstorm warning]].

In Canada, a severe thunderstorm is defined as either having tornadoes, wind gusts of 90 km/h or greater, hail of 2 centimeters in diameter or greater, a rainfall rate greater than 50 millimeters in 1 hour, or 75 millimeters in 3 hours.<ref>[http://www.on.ec.gc.ca/severe-weather/summerwx_factsheet_e.html Summer weather factsheet English<!-- Bot generated title -->]</ref>

Severe thunderstorms can occur from any type of thunderstorm, however multicell and squall lines represent the most common forms. Supercells are often the most powerful type of severe thunderstorm.

===Back-building thunderstorm===
A back-building thunderstorm is a thunderstorm in which new development takes place on the upwind side (usually the west or southwest side in [[North America]]), such that the storm seems to remain stationary or propagate in a backward direction. Although the storm often appears to be stationary or even moving upwind on radar, this is actually an illusion. The storm in reality is a multi-cell storm with new, more vigorous, cells being formed on the upwind side replacing older cells which continue to drift downstream.<ref>[http://www.srh.noaa.gov/jetstream/tstorms/tstrmtypes.htm NWS Jetstream - Types of Thunderstorms]</ref>

==Mesoscale Convective System==
Multicell or squall line systems may form within a meteorologically important feature known as [[Mesoscale Convective System]] (MCS) stretching for hundreds of kilometers. The [[Mesoscale Convective Complex]] is a closely related phenomenon. They are large enough to have a pronounced effect on the upper-level and surface weather pattern and may influence forecasts over a large area. MCS systems are common in the [[Midwestern United States]] and the [[Canadian Prairies]] during the summer months and produce much of the region's important agricultural rainfall. <ref>[http://www.mcema.net/thunderstorms.asp Mobile County Emergency Management Agency<!-- Bot generated title -->]</ref> Prior to the discovery of the MCS phenomenon, the individual thunderstorms were thought of as independent entities, each being effectively impossible to predict. The MCS is amenable to forecasting, and a meteorologist can predict with high accuracy the percentage of the MCS that will be affected by thunderstorms. However, the meteorologist still cannot predict exactly where each thunderstorm will occur within the MCS.

==Energy==
[[Image:Thunder lightning Garajau Madeira 289985700.jpg|thumb|225px|Thunderstorm over Garajau, [[Madeira]]]]
If the quantity of water that is condensed in and subsequently precipitated from a cloud is known, then the total energy of a thunderstorm can be calculated. In an average thunderstorm, the energy released amounts to about 10,000,000 kilowatt-hours (3.6{{e|13}} [[joule]]), which is equivalent to a 20-kiloton [[nuclear weapon|nuclear warhead]]. A large, severe thunderstorm might be 10 to 100 times more energetic.<ref>''[[Encyclopedia Britannica]]'' article on thunderstorms</ref>
<br style="clear:right;"/>

==Where thunderstorms occur==
[[Image:Example of a cold front.svg|thumb|Illustration of a cold front]]
Thunderstorms occur throughout the world, even in the polar regions, with the greatest frequency in [[tropical]] [[rainforest]] areas, where they may occur nearly daily. [[Kampala]] and [[Tororo]] in [[Uganda]] have each been mentioned as the most thunderous places on Earth,<ref>{{cite web | url = http://sky-fire.tv/index.cgi/thunderstorms.html#occur | title = How many thunderstorms occur each year? | work = Thunderstorms | publisher = Sky Fire Productions | accessdate = 2006-08-23}}</ref> an accolade which has also been bestowed upon [[Bogor]] on [[Java (island)|Java]], [[Indonesia]] or [[Singapore]]. Thunderstorms are associated with the various [[monsoon]] seasons around the globe, and they populate the rainbands of all{{Fact|date=May 2008}} [[tropical cyclone]]s. In temperate regions, they are most frequent in spring and summer, although they can occur along or ahead of cold fronts at any time of year. They may also occur within a cooler air mass following the passage of a cold front over a relatively warmer body of water. Thunderstorms are rare in polar regions because of cold surface temperatures.

<!--(should be moved to Climate of the United States)-->
Some of the most powerful and dangerous thunderstorms occur over the United States, particularly in the Midwest and the [[Southern United States|southern states]]. These storms can produce large hail and powerful tornadoes. Thunderstorms are relatively uncommon along much of the [[West Coast of the United States]],<ref>{{cite web |url=http://www.ofcm.gov/slso/pdf/slsochp2.pdf |title=National Severe Local Storms Operations Plan - Chapter 2 |format=PDF |publisher=Office of the Federal Coordinator for Meteorology |accessdate=2006-08-23}}</ref> but they occur with greater frequency in the inland areas, particularly the [[Sacramento Valley|Sacramento]] and [[San Joaquin Valley|San Joaquin]] Valleys of [[California]]. Furthermore, in spring and summer, they occur nearly daily in certain areas of the [[Rocky Mountains]]. In the [[Northeastern United States|Northeast]], storms take on similar characteristics and patterns as the Midwest, only less frequently and severely. Probably the most thunderous region outside of the Tropics is [[Florida]]. During the summer, violent thunderstorms are an almost daily occurrence over central and southern parts of the state. In more contemporary times, thunderstorms have taken on the role of a curiosity. Every spring, [[storm chasing|storm chasers]] head to the [[Great Plains]] of the United States and the Canadian Prairies to explore the visual and scientific aspects of storms and tornadoes.

==Lightning==
[[Image:Lightning in Arlington.jpg|thumb|right|Cloud to ground lightning over [[Pentagon City, Arlington, Virginia|Pentagon City]] in [[Arlington County, Virginia|Arlington]], [[Virginia]]]]
<!-- Unsourced image removed: [[Image:Tamworth Lightning FearTec.jpg|thumb|right|Fork lightning over [[Tamworth, New South Wales]] in Australia]] -->
[[Image:Thunderstorm in sydney 2000x1500.png|thumb|right|Lightning storm over [[Sydney, New South Wales]] in Australia]]

[[Lightning]] is an electrical discharge that occurs in a thunderstorm. It can be seen in the form of a bright streak (or bolt) from the sky. Lightning occurs when an [[electrical charge]] is built up within a cloud, due to static electricity generated by [[supercooling|supercooled]] [[water droplet]]s colliding with [[ice crystal]]s near the [[freezing level]]. When a large enough charge is built up, a large discharge will occur and can be seen as lightning. The temperature of a lightning bolt can be five times hotter than the surface of the sun.<ref>{{cite web | title = Lightning | publisher = BBC | url = http://www.bbc.co.uk/weather/features/understanding/lightning.shtml | accessdate = 2008-06-29 }}</ref> Although the lightning is extremely hot, the duration is short and 90% of strike victims survive. Contrary to the popular idea that lightning does not strike twice in the same spot, some people have been struck by lightning over three times, and skyscrapers like the [[Empire State Building]] have been struck numerous times in the same storm.<ref>[http://www.nasa.gov/centers/goddard/news/topstory/2003/0107lightning.html "Lightning really does hit more than twice,"], ''[[NASA]]'', [[January 14]], [[2003]]</ref>
The loud bang that is heard is the super heated air around the lightning bolt expanding at the [[speed of sound]]. Because sound travels slower than light the flash is seen before the bang, although both occur at the same moment.
There are several types of lightning:
*In-cloud lightning is the most common. It is lightning within a cloud and is sometimes called intra-cloud or sheet lightning.
*Cloud to ground lightning is when a bolt of lightning from a cloud strikes the ground. This form poses the greatest threat to life and property.
*Ground to cloud lightning is when a lightning bolt is induced from the ground to the cloud.
*Cloud to cloud lightning is rarely seen and is when a bolt of lightning arcs from one cloud to another.
*[[Ball lightning]] is extremely rare and has several hypothesized explanations. It is seen in the form of a 20 to 200 centimeter ball.
*Cloud to air lightning is when lightning from a cloud hits air of a different charge.
*[[Dry lightning]] is a misnomer which refers to a thunderstorm whose precipitation does not reach the ground.

==Mythology==
{{Expand|section|date=October 2008}}
Thunderstorms have had a lasting and powerful influence on early civilizations. [[Ancient Rome|Romans]] thought them to be battles waged by [[Jupiter (god)|Jupiter]], who hurled lightning bolts forged by [[Vulcan (mythology)|Vulcan]]. Thunderstorms were associated with the [[Thunderbird (mythology)|Thunderbirds]], held by [[Indigenous peoples of the Americas|Native Americans]] to be a servant of the [[Great Spirit]].<ref>[http://web.raex.com/~obsidian/HaudPan.html "A Haudenosaunee Pantheon "]</ref> [[Mjolnir]], the hammer of the Germanic and Nordic god of thunder, [[Thor]], had the ability to throw lightning bolts.

== See also ==
* [[Convective storm detection]]
* [[Cumulonimbus]]
* [[Severe thunderstorm warning]] and [[Severe thunderstorm watch]]
* [[Storm train]]
* [[Supercell]]
* [[Thunder]]
* [[Thundersnow]]
* [[Tornado warning]] and [[Tornado watch]]

==References==
{{Weather nav}}
{{reflist|2}}
<div class="references-small">
:*Burgess, D.W., R. J. Donaldson Jr., and P. R. Desrochers, 1993: ''Tornado detection and warning by radar. The Tornado: Its Structure, Dynamics, Prediction, and Hazards, Geophys. Monogr.'', No. 79, [[American Geophysical Union]], 203–221.
:*Corfidi, S. F., 1998: ''Forecasting MCS mode and motion.'' Preprints 19th Conf. on Severe Local Storms, [[American Meteorological Society]], [[Minneapolis]], Minnesota, pp. 626-629.
:*Davies, J.M., 2004:'' Estimations of CIN and LFC associated with tornadic and nontornadic supercells''. Wea. Forecasting, 19, 714-726.
:*Davies, J.M., and R. H. Johns, 1993: ''Some wind and instability parameters associated with strong and violent tornadoes. Part I: Helicity and mean shear magnitudes. The Tornado: Its Structure, Dynamics, Prediction, and Hazards'' (C. Church et al., Eds.), Geophysical Monograph 79, American Geophysical Union, 573-582.
:*David, C.L. 1973: ''An objective of estimating the probability of severe thunderstorms''. Preprint Eight conference of Severe Local Storms. [[Denver, Colorado]], [[American Meteorological Society]], 223-225.
:*Doswell, C.A., III, D. V. Baker, and C. A. Liles, 2002: ''Recognition of negative factors for severe weather potential: A case study''. Wea. Forecasting, 17, 937–954.
:*Doswell, C.A., III, S.J. Weiss and R.H. Johns (1993): ''Tornado forecasting: A review. The Tornado: Its Structure, Dynamics, Prediction, and Hazards (C. Church et al., Eds)'', Geophys. Monogr. No. 79, American Geophysical Union, 557-571.
:*Johns, R. H., J. M. Davies, and P. W. Leftwich, 1993: ''Some wind and instability parameters associated with strong and violent tornadoes. Part II: Variations in the combinations of wind and instability parameters. The Tornado: Its Structure, Dynamics, Prediction and Hazards, Geophys. Mongr.'', No. 79, American Geophysical Union, 583–590.
</div>

==Further reading==
*Evans, Jeffry S.: ''Examination of Derecho Environments Using Proximity Soundings''. [http://www.spc.noaa.gov/publications/evans/bowpaper/bowpaper.htm]
*J.V. Iribarne and W.L. Godson, ''Atmospheric Thermodynamics'', published by D. Reidel Publishing Company, [[Dordrecht]], the [[Netherlands]], 1973, 222 pages
*M K Yau and R.R. Rogers, ''Short Course in Cloud Physics, Third Edition'', published by Butterworth-Heinemann, [[January 1]], [[1989]], 304 pages. EAN 9780750632157 ISBN 0-7506-3215-1

==External links==
{{Commons|Thunderstorm}}
*[http://www.canadiangeographic.ca/atlas/themes.aspx?id=weather&sub=weather_phenomena_thunderstorm&lang=En Anatomy of a thunderstorm]
*[http://www.ejssm.org/ Electronic Journal of Severe Storms Meteorology]
*[http://www.ncdc.noaa.gov/oa/esb/?goal=weather&file=events/storm/ Social & Economic Costs of Thunderstorms & High Winds] from "NOAA Socioeconomics" website initiative
*[http://www.wetter-foto.de/fotos-5-1-all-Gewitterwolken.html Thunderstorm photography in Germany]

{{Meteorological variables}}

[[Category:Storms]]
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[[Category:Severe weather and convection]]
[[Category:Weather hazards]]

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Revision as of 14:22, 21 October 2008