Thunderstorm#Severe thunderstorms

File:Thunderstorm formation.jpg

{{See also|Cloud}}

Warm air has a lower density than cool air, so warmer air rises upwards and cooler air will settle at the bottom{{cite book|url=https://archive.org/details/civilengineersp00fryegoog |title=Civil engineers' pocket book: a reference-book for engineers, contractors|author=Albert Irvin Frye|page=[https://archive.org/details/civilengineersp00fryegoog/page/n500 462]|publisher=D. Van Nostrand Company|date=1913|access-date=31 August 2009}} (this effect can be seen with a hot air balloon).{{cite book|url= https://books.google.com/books?id=ssO_19TRQ9AC&pg=PA112 |title=Ancient Chinese Inventions

| author = Yikne Deng

| publisher = Chinese International Press

| isbn=978-7-5085-0837-5

| date=2005

| pages = 112–13|access-date=18 June 2009}} Clouds form as relatively warmer air, carrying moisture, rises within cooler air. The moist air rises, and, as it does so, it cools and some of the water vapor in that rising air condenses.{{cite web|author=FMI|date=2007|url=http://www.zamg.ac.at/docu/Manual/SatManu/main.htm?/docu/Manual/SatManu/CMs/FgStr/backgr.htm |title=Fog And Stratus – Meteorological Physical Background|publisher=Zentralanstalt für Meteorologie und Geodynamik|access-date=7 February 2009}} When the moisture condenses, it releases energy known as latent heat of condensation, which allows the rising packet of air to cool less than the cooler surrounding air{{cite book|url=https://archive.org/details/stormworldhurric00moon |url-access=registration |title=Storm world: hurricanes, politics, and the battle over global warming|author=Chris C. Mooney|page=[https://archive.org/details/stormworldhurric00moon/page/20 20]|isbn=978-0-15-101287-9|publisher=Houghton Mifflin Harcourt|date=2007|access-date=31 August 2009}} continuing the cloud's ascension. If enough instability is present in the atmosphere, this process will continue long enough for cumulonimbus clouds to form and produce lightning and thunder. Meteorological indices such as convective available potential energy (CAPE) and the lifted index can be used to assist in determining potential upward vertical development of clouds.{{cite journal|author=David O. Blanchard|title=Assessing the Vertical Distribution of Convective Available Potential Energy|journal=Weather and Forecasting|volume=13|issue=3|pages=870–7|publisher=American Meteorological Society|date=September 1998|doi= 10.1175/1520-0434(1998)013<0870:ATVDOC>2.0.CO;2|bibcode= 1998WtFor..13..870B|s2cid=124375544 |url=https://zenodo.org/record/1234637|doi-access=free}} Generally, thunderstorms require three conditions in order to form:

1. Moisture
2. An unstable airmass
3. A lifting force (heat)

All thunderstorms, regardless of type, go through three stages: the developing stage, the mature stage, and the dissipation stage.{{cite web |title=Thunderstorm Basics |url=https://www.nssl.noaa.gov/education/svrwx101/thunderstorms/#:~:text=The%20developing%20stage%20of%20a,this%20stage%20but%20occasional%20lightning. |website=NOAA National Severe Storms Laboratory |access-date=14 January 2021 |language=EN-US}}{{cite book|title=Extreme Weather|author=Michael H. Mogil|date=2007|publisher=Black Dog & Leventhal Publisher|location=New York|isbn=978-1-57912-743-5|pages=[https://archive.org/details/extremeweatherun0000mogi/page/210 210–211]|url=https://archive.org/details/extremeweatherun0000mogi/page/210}} The average thunderstorm has a {{convert|24|km|mi|abbr=on}} diameter. Depending on the conditions present in the atmosphere, each of these three stages take an average of 30 minutes.{{cite web|url=http://www.nssl.noaa.gov/primer/tstorm/tst_basics.html|title=A Severe Weather Primer: Questions and Answers about Thunderstorms|author=National Severe Storms Laboratory|publisher=National Oceanic and Atmospheric Administration|date=15 October 2006|access-date=1 September 2009|archive-date=25 August 2009|archive-url=https://web.archive.org/web/20090825000832/http://www.nssl.noaa.gov/primer/tstorm/tst_basics.html|url-status=dead}}

File:Cumulus congestus to cumulonimbus incus.png' transformation into a mature cumulonimbus incus]]

The first stage of a thunderstorm is the cumulus stage or developing stage. During this stage, masses of moisture are lifted upwards into the atmosphere. The trigger for this lift can be solar illumination, where the heating of the ground produces thermals, or where two winds converge forcing air upwards, or where winds blow over terrain of increasing elevation. The moisture carried upward cools into liquid drops of water due to lower temperatures at high altitude, which appear 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, drier air. The air tends to rise in an updraft through the process of convection (hence the term convective precipitation). This process creates a low-pressure zone within and beneath the forming thunderstorm. In a typical thunderstorm, approximately 500 million kilograms of water vapor are lifted into the Earth's atmosphere.{{cite web|url=http://physics.syr.edu/courses/modules/ENERGY/ENERGY_POLICY/tables.html |title=Rough Values of Various Processes |author=Gianfranco Vidali |date=2009 |access-date=31 August 2009 |publisher=Syracuse University |url-status=dead |archive-url=https://web.archive.org/web/20100315113421/http://physics.syr.edu/courses/modules/ENERGY/ENERGY_POLICY/tables.html |archive-date=15 March 2010 }}{{failed verification|date=April 2024|reason=The source is a list of power values, none of which pertain to thunderstorm moisture or energy.}}

File:Anvil shaped cumulus panorama edit crop.jpg

In the mature stage of a thunderstorm, the warmed air continues to rise until it reaches an area of warmer air and can rise no farther. 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 coalesce into larger and heavier 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 become so large that they do not melt completely but fall as hail. While updrafts are still present, the falling rain drags the surrounding air with it, creating downdrafts as well. The simultaneous presence of both an updraft and a downdraft marks the mature stage of the storm and produces cumulonimbus clouds. During this stage, considerable internal turbulence can occur, which manifests as strong winds, severe lightning, and even tornadoes.{{cite web|url=http://www.pilotsweb.com/wx/w_sense.htm|title=Structural Icing in VMC|author=Pilot's Web The Aviator's Journal|date=13 June 2009|access-date=2 September 2009|archive-date=19 August 2011|archive-url=https://web.archive.org/web/20110819055501/http://pilotsweb.com/wx/w_sense.htm|url-status=dead}}

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 or direction, the downdraft will be separated from the updraft, and the storm may become a supercell, where the mature stage can sustain itself for several hours.

{{clear}}

File:Single-cell Thunderstorm in a No-shear Environment..jpg

File:Flanking line on dissipating cumulonimbus incus cloud.jpg in front of a dissipating cumulonimbus incus cloud]]

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. This phenomenon is known as a downburst. 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. Thunderstorms in an atmosphere with virtually no vertical wind shear weaken as soon as they send out an outflow boundary in all directions, which then quickly cuts off its inflow of relatively warm, moist air, and kills the thunderstorm's further growth.{{cite web|author=The Weather World 2010 Project|publisher=University of Illinois|url=http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/svr/comp/wind/home.rxml|title=Vertical Wind Shear|access-date=21 October 2006|date=3 September 2009}} The downdraft hitting the ground creates an outflow boundary. This can cause downbursts, a potential hazardous condition for aircraft to fly through, as a substantial change in wind speed and direction occurs, resulting in a decrease of airspeed and the subsequent reduction in lift for the aircraft. The stronger the outflow boundary is, the stronger the resultant vertical wind shear becomes.{{cite book|author=T. T. Fujita|date=1985|title=The Downburst, microburst and macroburst: SMRP Research Paper 210|author-link=Ted Fujita}}

File:CAPE vs SHEAR.svg

There are four main types of thunderstorms: single-cell, multi-cell, squall line (also called multi-cell line) and supercell. Which type forms depends on the instability and relative wind conditions at different layers of the atmosphere ("wind shear"). Single-cell thunderstorms form in environments of low vertical wind shear and last only 20–30 minutes.

Organized thunderstorms and thunderstorm clusters/lines can have longer life cycles as they form in environments of significant vertical wind shear, normally greater than {{convert|25|kn|m/s}} in the lowest {{convert|6|km|mi}} of the troposphere,Markowski, Paul and Yvette Richardson. Mesoscale Meteorology in Midlatitudes. John Wiley & Sons, Ltd., 2010.

pp. 209. which aids the development of stronger updrafts as well as various forms of severe weather. The supercell is the strongest of the thunderstorms, most commonly associated with large hail, high winds, and tornado formation. Precipitable water values of greater than {{convert|31.8|mm|in}} favor the development of organized thunderstorm complexes.{{cite journal | author = Maddox R.A., Chappell C.F., Hoxit L.R. | year = 1979 | title = Synoptic and meso-α scale aspects of flash flood events | journal = Bull. Amer. Meteor. Soc. | volume = 60 | issue = 2| pages = 115–123 | doi = 10.1175/1520-0477-60.2.115 | bibcode = 1979BAMS...60..115M | doi-access = free }} Those with heavy rainfall normally have precipitable water values greater than {{convert|36.9|mm|in}}.Schnetzler, Amy Eliza. Analysis of Twenty-Five Years of Heavy Rainfall Events in the Texas Hill Country. University of Missouri-Columbia, 2008. pp. 74. Upstream values of CAPE of greater than 800 J/kg are usually required for the development of organized convection.Markowski, Paul and Yvette Richardson. Mesoscale Meteorology in Midlatitudes. John Wiley & Sons, Ltd., 2010. pp. 215, 310.

{{Main|Air-mass thunderstorm}}

File:Thunderstorm over Wagga Wagga.jpg]]

This term technically applies to a single thunderstorm with one main updraft. Also known as air-mass thunderstorms, these are the typical summer thunderstorms in many temperate locales. They also occur in the cool unstable air that often follows the passage of a cold front from the sea during winter. Within a cluster of thunderstorms, the term "cell" refers to each separate principal updraft. Thunderstorm cells occasionally form in isolation, as the occurrence of one thunderstorm can develop an outflow boundary that sets up new thunderstorm development. Such storms are rarely severe and are a result of local atmospheric instability; hence the term "air mass thunderstorm". When such storms have a brief period of severe weather associated with them, it is known as a pulse severe storm. Pulse severe storms are poorly organized and occur randomly in time and space, making them difficult to forecast. Single-cell thunderstorms normally last 20–30 minutes.

{{Main|Multicellular thunderstorm}}

File:8402 STS41B Challenger Thunderstorms over Brazil.jpg]]

This is the most common type of thunderstorm development. Mature thunderstorms are found near the center of the cluster, while dissipating thunderstorms exist on their downwind side. Multicell storms form as clusters of storms but may then evolve into one or more squall lines. While each cell of the cluster may only last 20 minutes, the cluster itself may persist for hours at a time. They often arise from convective updrafts in or near mountain ranges and linear weather boundaries, such as strong cold fronts or troughs of low pressure. These type of storms are stronger than the single-cell storm, yet much weaker than the supercell storm. Hazards with the multicell cluster include moderate-sized hail, flash flooding, and weak tornadoes.

{{Main|Squall line}}

{{See also|List of derecho events}}

A squall line is an elongated line of severe thunderstorms that can form along or ahead of a cold front.{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=squall-line1|author=Glossary of Meteorology|title=Squall line|date=2009|access-date=14 June 2009|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20081217175139/http://amsglossary.allenpress.com/glossary/search?id=squall-line1|archive-date=17 December 2008}}{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=prefrontal-squall-line1|author=Glossary of Meteorology|title=Prefrontal squall line|date=2009|access-date=14 June 2009|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20070817224959/http://amsglossary.allenpress.com/glossary/search?id=prefrontal-squall-line1|archive-date=17 August 2007}} In the early 20th century, the term was used as a synonym for cold front.{{cite web|author=University of Oklahoma|date=2004|url=http://weather.ou.edu/~metr4424/Files/Norwegian_Cyclone_Model.pdf|title=The Norwegian Cyclone Model|access-date=17 May 2007 |archive-url = https://web.archive.org/web/20060901163934/http://weather.ou.edu/~metr4424/Files/Norwegian_Cyclone_Model.pdf |archive-date = 1 September 2006}} The squall line contains heavy precipitation, hail, frequent lightning, strong straight line winds, and possibly tornadoes and waterspouts.{{cite web|author=Office of the Federal Coordinator for Meteorology |date=2008 |url=http://www.ofcm.gov/slso/pdf/slsochp2.pdf |title=Chapter 2: Definitions |pages=2–1 |publisher=NOAA |access-date=3 May 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090506002006/http://www.ofcm.gov/slso/pdf/slsochp2.pdf |archive-date=6 May 2009 }} Severe weather in the form of strong straight-line winds can be expected in areas where the squall line itself is in the shape of a bow echo, within the portion of the line that bows out the most.{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=bow+echo&submit=Search|author=Glossary of Meteorology|title=Bow echo|date=2009|access-date=14 June 2009|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20110606103620/http://amsglossary.allenpress.com/glossary/search?p=1&query=bow+echo&submit=Search|archive-date=6 June 2011}} Tornadoes can be found along waves within a line echo wave pattern, or LEWP, where mesoscale low pressure areas are present.{{cite book|author=Glossary of Meteorology|date=2009|url=http://amsglossary.allenpress.com/glossary/search?id=line-echo-wave-pattern1|title=Line echo wave pattern|publisher=American Meteorological Society|isbn=978-1-878220-34-9|access-date=3 May 2009|url-status=dead|archive-url=https://web.archive.org/web/20080924175030/http://amsglossary.allenpress.com/glossary/search?id=line-echo-wave-pattern1|archive-date=24 September 2008}} Some bow echoes in the summer are called derechos, and move quite fast through large sections of territory.{{cite web| url=http://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm| title=About Derechos| publisher=Storm Prediction Center, NCEP, NWS, NOAA Web Site| author= Stephen F. Corfidi| author2= Jeffry S. Evans| author3= Robert H. Johns| name-list-style= amp | date=2015| access-date=17 February 2015}} On the back edge of the rain shield associated with mature squall lines, a wake low can form, which is a mesoscale low pressure area that forms behind the mesoscale high pressure system normally present under the rain canopy, which are sometimes associated with a heat burst.{{cite book |author= Glossary of Meteorology |title= Heat burst |publisher= American Meteorological Society |date= 2009 |url= http://amsglossary.allenpress.com/glossary/search?id=heat-burst1 |isbn= 978-1-878220-34-9 |access-date= 14 June 2009 |url-status= dead |archive-url= https://web.archive.org/web/20110606102146/http://amsglossary.allenpress.com/glossary/search?id=heat-burst1 |archive-date= 6 June 2011 }} This kind of storm is also known as "Wind of the Stony Lake" ({{Lang-zh|s=石湖风|t=石湖風}}; shi2 hu2 feng1) in southern China.{{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 | access-date = 23 August 2006 | archive-date = 25 October 2019 | archive-url = https://web.archive.org/web/20191025222307/http://www.hko.gov.hk/education/edu01met/wxphe/ele_squalle.htm | url-status = dead }}

{{Main|Supercell}}

File:Thunderhead.anvil.jpg, United States.]]

Supercell storms are large, usually severe, quasi-steady-state storms that form in an environment where wind speed or wind direction varies with height ("wind shear"), and they have separate downdrafts and updrafts (i.e., where its associated precipitation is not falling through the updraft) with a strong, rotating updraft (a "mesocyclone"). These storms normally have such powerful updrafts that the top of the supercell storm cloud (or anvil) can break through the troposphere and reach into the lower levels of the stratosphere. Supercell storms can be {{convert|24|km|mi|0}} wide. Research has shown that at least 90 percent of supercells cause severe weather.{{cite web|url=http://www.crh.noaa.gov/images/unr/soo/scm/ZB06.pdf|title=Operational Forecasting of Supercell Motion: Review and Case Studies Using Multiple Datasets|author=Jon W. Zeitler|author2=Matthew J. Bunkers|name-list-style=amp|date=March 2005|access-date=30 August 2009|publisher=National Weather Service Forecast Office, Riverton, Wyoming}} These storms can produce destructive tornadoes, extremely large hailstones ({{convert|10|cm|in|0|disp=or}} diameter), straight-line winds in excess of {{convert|130|km/h|mph|abbr=on}}, and flash floods. In fact, research has shown that most tornadoes occur from this type of thunderstorm.{{cite web|date=4 October 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|access-date=23 August 2006}} Supercells are generally the strongest type of thunderstorm.

In the United States, a thunderstorm is classed as severe if winds reach at least {{convert|93|km/h|mph}}, hail is {{convert|25|mm|in|0}} in diameter or larger, or if funnel clouds or tornadoes are reported.{{cite web | title =Weather Glossary – S | author =National Weather Service | author-link =National Weather Service | publisher=National Oceanic and Atmospheric Administration | date =21 April 2005 | url =http://www.weather.gov/glossary/index.php?letter=s | access-date =17 June 2007 }}{{cite video | people = Kim Runk | title = 1" Hail | medium = .wmv | publisher = NOAA | location = Silver Spring, Maryland|url= http://www.crh.noaa.gov/crh/One_Inch_Hail_Podcast.wmv |date = 2009}}{{cite web|url=http://www.wrh.noaa.gov/psr/pns/2009/April/NewHailCriteria.php?wfo=psr|author=National Weather Service Forecast Office, Phoenix, Arizona|title=New Hail Criteria|access-date=3 September 2009|date=7 April 2009}} Although a funnel cloud or tornado indicates a severe thunderstorm, a tornado warning is issued in place of a severe thunderstorm warning. A severe thunderstorm warning is issued if a thunderstorm becomes severe, or will soon turn severe. In Canada, a rainfall rate greater than {{convert|50|mm|in|0}} in one hour, or {{convert|75|mm|in|0}} in three hours, is also used to indicate severe thunderstorms.{{cite web|url=http://www.on.ec.gc.ca/severe-weather/summerwx_factsheet_e.html |title=Fact Sheet – Summer Severe Weather Warnings |author=Environment Canada Ontario Region |date=24 May 2005 |access-date=3 September 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090228151724/http://www.on.ec.gc.ca/severe-weather/summerwx_factsheet_e.html |archive-date=28 February 2009 }} Severe thunderstorms can occur from any type of storm cell. However, multicell, supercell, and squall lines represent the most common forms of thunderstorms that produce severe weather.

{{See also|Mesoscale convective system}}

File:June 2022 Midwest Mesoscale convective complex-derecho.jpg: on 13 June 2022, at 18:45 UTC]]

A mesoscale convective system (MCS) is a complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms but smaller than extratropical cyclones, and normally persists for several hours or more.{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=mesoscale+convective+system&submit=Search|title=Mesoscale convective system|date=2009|access-date=27 June 2009|author=Glossary of Meteorology|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20110606103649/http://amsglossary.allenpress.com/glossary/search?p=1&query=mesoscale+convective+system&submit=Search|archive-date=6 June 2011}} A mesoscale convective system's overall cloud and precipitation pattern may be round or linear in shape, and include weather systems such as tropical cyclones, squall lines, lake-effect snow events, polar lows, and mesoscale convective complexes (MCCs), and they generally form near weather fronts. Most mesoscale convective systems develop overnight and continue their lifespan through the next day. They tend to form when the surface temperature varies by more than {{convert|5|C-change|sigfig=1}} between day and night.{{cite journal |last1 = Haerter |first1 = Jan O. |last2 = Meyer| first2 = Bettina| last3 = Nissen| first3 = Silas Boye |title=Diurnal self-aggregation |journal=npj Climate and Atmospheric Science |date=30 July 2020 |volume=3 |issue = 1 |page = 30 |doi=10.1038/s41612-020-00132-z |arxiv= 2001.04740 |bibcode = 2020npCAS...3...30H |s2cid = 220856705 }} The type that forms during the warm season over land has been noted across North America, Europe, and Asia, with a maximum in activity noted during the late afternoon and evening hours.{{cite web|author=William R. Cotton|author2=Susan van den Heever|author3=Israel Jirak|name-list-style=amp|date=2003|url=http://rams.atmos.colostate.edu/at540/fall03/fall03Pt9.pdf|title=Conceptual Models of Mesoscale Convective Systems: Part 9|publisher=Colorado State University|access-date=23 March 2008}}{{cite journal|author=C. Morel|author2=S. Senesi|name-list-style=amp|date=2002|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=13876728 |title=A climatology of mesoscale convective systems over Europe using satellite infrared imagery II: Characteristics of European mesoscale convective systems|journal=Quarterly Journal of the Royal Meteorological Society|issn=0035-9009|access-date=2 March 2008|volume=128|issue=584|page=1973|doi=10.1256/003590002320603494|bibcode = 2002QJRMS.128.1973M |s2cid=120021136 |doi-access=free}}

Forms of MCS that develop in the tropics are found in use either the Intertropical Convergence Zone or monsoon troughs, generally within the warm season between spring and fall. More intense systems form over land than over water.{{cite journal|author=Semyon A. Grodsky|author2=James A. Carton|name-list-style=amp|url=http://www.atmos.umd.edu/~carton/pdfs/grodsky&carton03.pdf|date=15 February 2003|publisher=University of Maryland, College Park|title=The Intertropical Convergence Zone in the South Atlantic and the Equatorial Cold Tongue|journal=Journal of Climate|volume=16|issue=4|pages=723|access-date=5 June 2009|bibcode=2003JCli...16..723G|doi=10.1175/1520-0442(2003)016<0723:TICZIT>2.0.CO;2|s2cid=10083024 }}{{cite book|url=https://books.google.com/books?id=HiaP4yJ8wNMC&pg=PA40|title=Observations of surface to atmosphere interactions in the tropics|author=Michael Garstang|author2=David Roy Fitzjarrald|pages=40–41|date=1999|isbn=978-0-19-511270-2|publisher=Oxford University Press US}} One exception is that of lake-effect snow bands, which form due to cold air moving across relatively warm bodies of water, and occurs from fall through spring.{{cite web|author=B. Geerts|date=1998|url=http://www-das.uwyo.edu/~geerts/cwx/notes/chap10/lake_effect_snow.html|title=Lake Effect Snow|access-date=24 December 2008|publisher=University of Wyoming}} Polar lows are a second special class of MCS. They form at high latitudes during the cold season.{{cite book|author=E. A. Rasmussen|author2=J. Turner|name-list-style=amp|date=2003|title=Polar Lows: Mesoscale Weather Systems in the Polar Regions|publisher=Cambridge University Press|page=612|isbn=978-0-521-62430-5}} Once the parent MCS dies, later thunderstorm development can occur in connection with its remnant mesoscale convective vortex (MCV).{{cite web|title=3.5 The Influence of the Great Lakes on Warm Season Weather Systems During BAMEX|author=Lance F. Bosart|author2=Thomas J. Galarneau Jr.|name-list-style=amp|url=http://ams.confex.com/ams/pdfpapers/84665.pdf|publisher=6th American Meteorological Society Coastal Meteorology Conference|date=2005|access-date=15 June 2009}} Mesoscale convective systems are important to the United States rainfall climatology over the Great Plains since they bring the region about half of their annual warm season rainfall.{{cite web|author=William R. Cotton|author2=Susan van den Heever|author3=Israel Jirak|name-list-style=amp|url=http://rams.atmos.colostate.edu/at540/fall03/fall03Pt9.pdf|title=Conceptual Models of Mesoscale Convective Systems: Part 9|date=Fall 2003|access-date=23 March 2008}}

File:Sturmfront auf Doppler-Radar-Schirm.jpg (dBZ) on a plan position indicator radar display]]

The two major ways thunderstorms move are via advection of the wind and propagation along outflow boundaries towards sources of greater heat and moisture. Many thunderstorms move with the mean wind speed through the Earth's troposphere, the lowest {{convert|8|km|mi}} of the Earth's atmosphere. Weaker thunderstorms are steered by winds closer to the Earth's surface than stronger thunderstorms, as the weaker thunderstorms are not as tall. Organized, long-lived thunderstorm cells and complexes move at a right angle to the direction of the vertical wind shear vector. If the gust front, or leading edge of the outflow boundary, races ahead of the thunderstorm, its motion will accelerate in tandem. This is more of a factor with thunderstorms with heavy precipitation (HP) than with thunderstorms with low precipitation (LP). When thunderstorms merge, which is most likely when numerous thunderstorms exist in proximity to each other, the motion of the stronger thunderstorm normally dictates the future motion of the merged cell. The stronger the mean wind, the less likely other processes will be involved in storm motion. On weather radar, storms are tracked by using a prominent feature and tracking it from scan to scan.

A back-building thunderstorm, commonly referred to as a training thunderstorm, is a thunderstorm in which new development takes place on the upwind side (usually the west or southwest side in the Northern Hemisphere), such that the storm seems to remain stationary or propagate in a backward direction. Though the storm often appears stationary on radar, or even moving upwind, this is an illusion. The storm is really a multi-cell storm with new, more vigorous cells that form on the upwind side, replacing older cells that continue to drift downwind.{{cite web|url=http://www.spc.noaa.gov/publications/corfidi/mcsflashflood_2015feb07.ppt|title=MCS Movement and Behavior (PowerPoint)|author=Stephen Corfidi|publisher=National Weather Service, Storm Prediction Center|date=4 February 2015|access-date=18 February 2015}}{{cite web|url=http://www.srh.noaa.gov/jetstream/tstorms/tstrmtypes.htm|title=Types of Thunderstorms|author=National Weather Service|author-link=National Weather Service|publisher=National Weather Service Southern Region Headquarters|date=1 September 2009|access-date=3 September 2009}} 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 continuously training set of cells that dropped an enormous quantity of rain upon the same area, resulting in devastating flash flooding.{{cite web|url=http://www.crh.noaa.gov/unr/?n=weather|author=National Weather Service Forecast Office, Rapid City, South Dakota|title=The Rapid City Flood of 1972|publisher=National Weather Service Central Region Headquarters|access-date=3 September 2009|date=15 May 2007}} A similar event occurred in Boscastle, England, on 16 August 2004,{{cite web|url=http://www.tintagelweb.co.uk/BoscastleFlood.htm|title=Boscastle Flood 2004|author=David Flower|publisher=Tintagel – King Arthur Country|date=9 February 2008|access-date=3 September 2009}} and over Chennai on 1 December 2015.{{cite journal|title=Role of Eastern Ghats Orography and Cold Pool in an Extreme Rainfall Event over Chennai on 1 December 2015|journal=Monthly Weather Review|volume=146|issue=4|pages=943–965|author=Jayesh Phadtare|publisher=American Meteorological Society.|doi=10.1175/MWR-D-16-0473.1|year=2018|bibcode=2018MWRv..146..943P|doi-access=free}}

Each year, many people are killed or seriously injured by severe thunderstorms despite the advance warning{{citation needed|date=March 2019}}. While severe thunderstorms are most common in the spring and summer, they can occur at just about any time of the year.

{{See also|Lightning strike|Wildfire}}

File:Blitze IMGP6376 wp.jpg

Cloud-to-ground lightning frequently occurs within the phenomena of thunderstorms and have numerous hazards towards landscapes and populations. One of the more significant hazards lightning can pose is the wildfires they are capable of igniting.{{Cite journal | doi =10.1016/S0031-0182(00)00192-9 | title =The Pre-Quaternary history of fire | date =2000 | author =Scott, A | journal = Palaeogeography, Palaeoclimatology, Palaeoecology | volume =164 | issue =1–4 | page =281 | bibcode =2000PPP...164..281S }} Under a regime of low precipitation (LP) thunderstorms, where little precipitation is present, rainfall cannot prevent fires from starting when vegetation is dry as lightning produces a concentrated amount of extreme heat.{{cite web|url=http://plaza.ufl.edu/rakov/Gas.html|title=Lightning Makes Glass|access-date=7 November 2007|publisher=University of Florida, Gainesville|date=1999|author=Vladimir A. Rakov}} Direct damage caused by lightning strikes occurs on occasion.{{cite web|url=http://www.hughston.com/hha/a_12_3_4.htm|title=Lightning and Its Hazards|author=Bruce Getz|author2=Kelli Bowermeister|name-list-style=amp|publisher=Hughston Sports Medicine Foundation|date=9 January 2009|access-date=9 September 2009|url-status=dead|archive-url=https://web.archive.org/web/20100124020843/http://www.hughston.com/hha/a_12_3_4.htm|archive-date=24 January 2010}} In areas with a high frequency for cloud-to-ground lightning, like Florida, lightning causes several fatalities per year, most commonly to people working outside.{{cite web|url=http://ams.confex.com/ams/88Annual/techprogram/paper_132808.htm|title=P2.13 Florida lightning deaths and injuries 2004–2007|author=Charles H. Paxton|author2=J. Colson|author3=N. Carlisle|name-list-style=amp|publisher=American Meteorological Society|date=2008|access-date=5 September 2009}}

Acid rain is also a frequent risk produced by lightning. Distilled water has a neutral pH of 7. "Clean" or unpolluted rain has a slightly acidic pH of about 5.2, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid (pH 5.6 in distilled water), but unpolluted rain also contains other chemicals.{{cite journal|author=G. E. Likens|author2=W. C. Keene|author3=J. M. Miller|author4=J. N. Galloway|name-list-style=amp|date=1987|title=Chemistry of precipitation from a remote, terrestrial site in Australia|journal=Journal of Geophysical Research|volume=92|issue=13|pages=299–314|bibcode = 1987JGR....92..299R |doi = 10.1029/JA092iA01p00299 }} Nitric oxide present during thunderstorm phenomena,{{cite journal|author=Joel S. Levine|author2=Tommy R. Augustsson|author3=Iris C. Andersont|author4=James M. Hoell Jr.|author5=Dana A. Brewer|name-list-style=amp|date=1984|title=Tropospheric sources of NOx: Lightning and biology|journal=Atmospheric Environment|volume=18|issue=9|pages=1797–1804|bibcode=1984AtmEn..18.1797L|doi=10.1016/0004-6981(84)90355-X|pmid=11540827}} caused by the oxidation of atmospheric nitrogen, can result in the production of acid rain, if nitric oxide forms compounds with the water molecules in precipitation, thus creating acid rain. Acid rain can damage infrastructures containing calcite or certain other solid chemical compounds. In ecosystems, acid rain can dissolve plant tissues of vegetations and increase acidification process in bodies of water and in soil, resulting in deaths of marine and terrestrial organisms.{{cite web|author=Office of Air and Radiation Clean Air Markets Division|url=http://www.epa.gov/acidrain/effects/surface_water.html|title=Effects of Acid Rain – Surface Waters and own Aquatic Animals|access-date=5 September 2009|date=1 December 2008|publisher=United States Environmental Protection Agency}}

{{Main|Hail}}

File:Bogota hailstorm.jpg, Colombia]]

Any thunderstorm that produces hail that reaches the ground is known as a hailstorm.{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=Hailstorm|title=Hailstorm|author=Glossary of Meteorology|date=2009|access-date=29 August 2009|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20110606103908/http://amsglossary.allenpress.com/glossary/search?p=1&query=Hailstorm|archive-date=6 June 2011}} Thunderclouds that are capable of producing hailstones are often seen obtaining green coloration. Hail is more common along mountain ranges because mountains force horizontal winds upwards (known as orographic lifting), thereby intensifying the updrafts within thunderstorms and making hail more likely.{{cite web|url=http://www.ga.gov.au/hazards/severeweather/where.jsp|title=Where does severe weather occur?|author=Geoscience Australia|publisher=Commonwealth of Australia|access-date=28 August 2009|date=4 September 2007|archive-url=https://web.archive.org/web/20090621231613/http://www.ga.gov.au/hazards/severeweather/where.jsp |archive-date=21 June 2009}} One of the more common regions for large hail is across mountainous northern India, which reported one of the highest hail-related death tolls on record in 1888.{{cite book|url=https://books.google.com/books?id=-mwbAsxpRr0C&pg=PA401|title=Encyclopedia of World Climatology|author=John E. Oliver|page=401|publisher=Springer|isbn=978-1-4020-3264-6|date=2005|access-date=28 August 2009}} China also experiences significant hailstorms.{{cite journal|title=The characteristics of cloud-to-ground lightning activity in hailstorms over northern China |author=Dongxia Liu |author2=Guili Feng |author3=Shujun Wu |name-list-style=amp|date=February 2009|journal=Atmospheric Research|volume=91|issue=2–4|pages=459–465|doi=10.1016/j.atmosres.2008.06.016|bibcode = 2009AtmRe..91..459L }} Across Europe, Croatia experiences frequent occurrences of hail.{{cite journal|title=Hail characteristics of different regions in continental part of Croatia based on influence of orography|author=Damir Počakal|author2=Željko Večenaj|author3=Janez Štalec|name-list-style=amp|journal=Atmospheric Research|volume=93|issue=1–3|date=2009|doi=10.1016/j.atmosres.2008.10.017|page=516|bibcode = 2009AtmRe..93..516P }}

In North America, hail is most common in the area where Colorado, Nebraska, and Wyoming meet, known as "Hail Alley".{{cite web|url=http://www.ucar.edu/communications/factsheets/Hail.html|title=Fact Sheet on Hail|access-date=18 July 2009|author=Rene Munoz|date=2 June 2000|publisher=University Corporation for Atmospheric Research|url-status=dead|archive-url=https://web.archive.org/web/20091015141754/http://www.ucar.edu/communications/factsheets/Hail.html|archive-date=15 October 2009}} Hail in this region occurs between the months of March and October during the afternoon and evening hours, with the bulk of the occurrences from May through September. Cheyenne, Wyoming, is North America's most hail-prone city with an average of nine to ten hailstorms per season. In South America, areas prone to hail are cities like Bogotá, Colombia.

Hail can cause serious damage, notably to automobiles, aircraft, skylights, glass-roofed structures, livestock, and most commonly, farmers' crops.{{cite journal|url=http://www.cocorahs.org/media/docs/hail_1994.pdf|title=Hail, Hail, Hail ! The Summertime Hazard of Eastern Colorado|author=Nolan J. Doesken|journal=Colorado Climate|volume=17|issue=7|date=April 1994|access-date=18 July 2009|archive-date=25 November 2010|archive-url=https://web.archive.org/web/20101125163951/http://cocorahs.org/media/docs/hail_1994.pdf|url-status=dead}} Hail is one of the most significant thunderstorm hazards to aircraft. When hail stones exceed {{convert|13|mm|in|1}} in diameter, planes can be seriously damaged within seconds.{{cite web|url=http://www.aviationweather.ws/063_Hazards.php|title=Hazards|author=Federal Aviation Administration|author-link=Federal Aviation Administration|date=2009|access-date=29 August 2009}} The hailstones accumulating on the ground can also be hazardous to landing aircraft. Wheat, corn, soybeans, and tobacco are the most sensitive crops to hail damage. Hail is one of Canada's most costly hazards.{{cite book|url=https://books.google.com/books?id=s6oxEraqWWwC&pg=RA1-PA61|title=Introduction to international disaster management|author=Damon P. Coppola|page=62|date=2007|isbn=978-0-7506-7982-4|publisher=Butterworth-Heinemann}} Hailstorms have been the cause of costly and deadly events throughout history. One of the earliest recorded incidents occurred around the 9th century in Roopkund, Uttarakhand, India.{{cite web|url=https://www.telegraph.co.uk/news/main.jhtml?xml=/news/2004/11/07/wind07.xml&sSheet=/news/2004/11/07/ixworld.html |title=Giant hail killed more than 200 in Himalayas |author=David Orr |date=7 November 2004 |access-date=28 August 2009 |publisher=Telegraph Group Unlimited via the Internet Wayback Machine |archive-url=https://web.archive.org/web/20051203015218/http://www.telegraph.co.uk/news/main.jhtml?xml=%2Fnews%2F2004%2F11%2F07%2Fwind07.xml&sSheet=%2Fnews%2F2004%2F11%2F07%2Fixworld.html |archive-date=3 December 2005 |url-status=dead }} The largest hailstone in terms of maximum circumference and length ever recorded in the United States fell in 2003 in Aurora, Nebraska, United States.{{cite journal | author = Knight C. A., Knight N.C. | year = 2005 | title = Very Large Hailstones From Aurora, Nebraska | journal = Bull. Amer. Meteor. Soc. | volume = 86 | issue = 12| pages = 1773–1781 | doi = 10.1175/bams-86-12-1773 | bibcode = 2005BAMS...86.1773K | doi-access = free }}

File:F5 tornado Elie Manitoba 2007.jpg was struck by an F5 tornado.]]

{{Main|Tornado|Waterspout}}

A tornado is a violent, rotating column of air in contact with both the surface of the earth and a cumulonimbus cloud (otherwise known as a thundercloud) or, in rare cases, the base of a cumulus cloud. Tornadoes come in many sizes but are typically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud of debris and dust.{{cite journal |last = Renno |first = Nilton O. |title = A thermodynamically general theory for convective vortices |journal = Tellus A |volume = 60 |issue = 4 |pages = 688–99 |date=August 2008 |url = http://vortexengine.ca/misc/Renno_2008.pdf |doi = 10.1111/j.1600-0870.2008.00331.x |bibcode=2008TellA..60..688R|hdl = 2027.42/73164 |hdl-access = free }} Most tornadoes have wind speeds between {{convert|40|and|110|mph|km/h|abbr=on}}, are approximately {{convert|75|m|ft}} across, and travel several kilometers (a few miles) before dissipating. Some attain wind speeds of more than {{convert|300|mph|km/h|abbr=on}}, stretch more than {{convert|1600|m|mi|0}} across, and stay on the ground for more than 100 kilometres (dozens of miles).{{cite web| url = http://www.spc.noaa.gov/faq/tornado| title = The Online Tornado FAQ| access-date = 8 September 2006| last = Edwards| first = Roger |author-link= Roger Edwards (meteorologist) | date = 4 April 2006| publisher = Storm Prediction Center}}

{{cite web| url = http://cswr.org/dow/DOW.htm| title = Doppler On Wheels| access-date = 29 December 2006| publisher = Center for Severe Weather Research| date = 2006| url-status = dead| archive-url = https://web.archive.org/web/20070205124033/http://www.cswr.org/dow/dow.htm| archive-date = 5 February 2007}}{{cite web| url = http://www.crh.noaa.gov/oax/archive/hallam/hallam.php| title = Hallam Nebraska Tornado | access-date = 8 September 2006| publisher = Omaha/Valley, NE Weather Forecast Office | date = 2 October 2005}}

The Fujita scale and the Enhanced Fujita Scale rate tornadoes by damage caused. An EF0 tornado, the weakest category, damages trees but does not cause significant damage to structures. An EF5 tornado, the strongest category, rips buildings off their foundations and can deform large skyscrapers. The similar TORRO scale ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes.{{cite web|url=http://www.torro.org.uk/TORRO/ECSS_Slide_Show/2004%20SPAIN%20ECSS%20Post-FINAL%20slide%20show.html |title=Wind Scales: Beaufort, T – Scale, and Fujita's Scale |author=Dr. Terence Meaden |publisher=Tornado and Storm Research Organisation |date=2004 |access-date=11 September 2009 |url-status=dead |archive-url=https://web.archive.org/web/20100430211910/http://www.torro.org.uk/TORRO/ECSS_Slide_Show/2004%20SPAIN%20ECSS%20Post-FINAL%20slide%20show.html |archive-date=30 April 2010 }} Doppler radar data, photogrammetry, and ground swirl patterns (cycloidal marks) may also be analyzed to determine intensity and award a rating.{{cite web | title = Enhanced F Scale for Tornado Damage| author = Storm Prediction Center| publisher=National Oceanic and Atmospheric Administration| url = http://www.spc.noaa.gov/efscale/ef-scale.html| access-date = 21 June 2009 }}

File:Great Lakes Waterspouts.jpg region (North America)]]

Waterspouts have similar characteristics as tornadoes, characterized by a spiraling funnel-shaped wind current that form over bodies of water, connecting to large cumulonimbus clouds. Waterspouts are generally classified as forms of tornadoes, or more specifically, non-supercelled tornadoes that develop over large bodies of water.{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=Waterspout|title=Waterspout|date=2009|access-date=11 September 2009|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20080620115657/http://amsglossary.allenpress.com/glossary/search?p=1&query=waterspout|archive-date=20 June 2008}} These spiralling columns of air frequently develop within tropical areas close to the equator, but are less common within areas of high latitude.{{cite web|url=http://www.erh.noaa.gov/btv/events/15Jan2009/overview.shtml|title=15 January 2009: Lake Champlain Sea Smoke, Steam Devils, and Waterspout: Chapters IV and V|author=National Weather Service Forecast Office, Burlington, Vermont|publisher=Eastern Region Headquarters|date=3 February 2009|access-date=21 June 2009}}

{{Main|Flash flood}}

File:Kings Christian Church carpark Flooded.jpg

Flash flooding is the process where a landscape, most notably an urban environment, is subjected to rapid floods.{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=Flash+flood|title=Flash Flood|author=Glossary of Meteorology|publisher=American Meteorological Society|date=2009|access-date=9 September 2009|url-status=dead|archive-url=https://web.archive.org/web/20110606085246/http://amsglossary.allenpress.com/glossary/search?p=1&query=Flash+flood|archive-date=6 June 2011}} These rapid floods occur more quickly and are more localized than seasonal river flooding or areal flooding{{cite web|author=National Weather Service|title=Flood Products: What Do They Mean?|url=http://www.srh.noaa.gov/bmx/?n=outreach_flw|publisher=NOAA|access-date=23 August 2011}} and are frequently (though not always) associated with intense rainfall.{{cite web|author=National Weather Service|title=Flash Flood|url=http://www.crh.noaa.gov/glossary.php?word=FLASH%20FLOOD|publisher=NOAA|access-date=23 August 2011}} Flash flooding can frequently occur in slow-moving thunderstorms and is usually caused by the heavy liquid precipitation that accompanies it. Flash floods are most common in arid regions as well as densely populated urban environments, where few plants, and bodies of water are present to absorb and contain the extra water. Flash flooding can be hazardous to small infrastructure, such as bridges, and weakly constructed buildings. Plants and crops in agricultural areas can be destroyed and devastated by the force of raging water. Automobiles parked within affected areas can also be displaced. Soil erosion can occur as well, exposing risks of landslide phenomena.

{{Main|Downburst}}

File:Downburst damage.jpg]]

Downburst winds can produce numerous hazards to landscapes experiencing thunderstorms. Downburst winds are generally very powerful, and are often mistaken for wind speeds produced by tornadoes,{{cite web|url=http://www.erh.noaa.gov/cae/svrwx/downburst.htm|title=Downbursts...|date=27 January 2009|author=National Weather Service Forecast Office Columbia, South Carolina|publisher=National Weather Service Eastern Region Headquarters|access-date=9 September 2009}} due to the concentrated amount of force exerted by their straight-horizontal characteristic. Downburst winds can be hazardous to unstable, incomplete, or weakly constructed infrastructures and buildings. Agricultural crops, and other plants in nearby environments can be uprooted and damaged. Aircraft engaged in takeoff or landing can crash. Automobiles can be displaced by the force exerted by downburst winds. Downburst winds are usually formed in areas when high pressure air systems of downdrafts begin to sink and displace the air masses below it, due to their higher density. When these downdrafts reach the surface, they spread out and turn into the destructive straight-horizontal winds.

{{Main|Thunderstorm asthma}}

Thunderstorm asthma is the triggering of an asthma attack by environmental conditions directly caused by a local thunderstorm. During a thunderstorm, pollen grains can absorb moisture and then burst into much smaller fragments with these fragments being easily dispersed by wind. While larger pollen grains are usually filtered by hairs in the nose, the smaller pollen fragments are able to pass through and enter the lungs, triggering the asthma attack.{{cite journal | author = Suphioglu C | year = 1998 | title = Thunderstorm Asthma Due to Grass Pollen | journal = Int Arch Allergy Immunol | volume = 116 | issue = 4| pages = 253–260 | doi = 10.1159/000023953 | pmid = 9693274 | s2cid = 46754817 }}{{cite journal | author = Taylor P.E., Jonsson H. | year = 2004 | title = Thunderstorm asthma | journal = Curr Allergy Asthma Rep | volume = 4 | issue = 5| pages = 409–13 | doi = 10.1007/s11882-004-0092-3 | pmid = 15283882 | s2cid = 19351066 }}{{cite journal | author = Dabrera G, Murray V, Emberlin J, Ayres JG, Collier C, Clewlow Y, Sachon P | date = March 2013 | title = Thunderstorm asthma: an overview of the evidence base and implications for public health advice | journal = QJM | volume = 106 | issue = 3| pages = 207–17 | doi = 10.1093/qjmed/hcs234 | pmid = 23275386 | doi-access = free }}{{cite journal | author = D'Amato G, Vitale C, D'Amato M, Cecchi L, Liccardi G, Molino A, Vatrella A, Sanduzzi A, Maesano C, Annesi-Maesano I | date = March 2016 | title = Thunderstorm-related asthma: what happens and why | url = https://hal.sorbonne-universite.fr/hal-01314504/file/D%27Amato_2016_Thunderstorm%E2%80%90related.pdf| journal = Clin Exp Allergy | volume = 46 | issue = 3| pages = 390–6 | doi = 10.1111/cea.12709 | pmid = 26765082 | s2cid = 12571515 }}

{{See also|Emergency management|Tornado preparedness}}

Most thunderstorms come and go fairly uneventfully; however, any thunderstorm can become severe, and all thunderstorms, by definition, present the danger of lightning.{{cite web|author=American Red Cross|title=Thunderstorm Safety Checklist|url=http://www.redcross.org/www-files/Documents/pdf/Preparedness/checklists/Thunderstorm.pdf|publisher=American Red Cross|access-date=24 August 2011}} Thunderstorm preparedness and safety refers to taking steps before, during, and after a thunderstorm to minimize injury and damage.

Preparedness refers to precautions that should be taken before a thunderstorm. Some preparedness takes the form of general readiness (as a thunderstorm can occur at any time of the day or year).{{cite web|author=National Weather Service Weather Forecast Office|title=Thunderstorm|url=http://www.srh.noaa.gov/abq/?n=prepthunderstorms|work=Severe Weather Preparedness Information|publisher=NOAA|access-date=24 August 2011|location=Albuquerque, NM}} Preparing a family emergency plan, for example, can save valuable time if a storm arises quickly and unexpectedly.{{cite web|author=Federal Emergency Management Agency|title=Thunderstorms and Lightning|url=http://www.ready.gov/america/beinformed/thunderstorms.html|work=Ready|publisher=US Department of Homeland Security|access-date=24 August 2011|archive-url=https://web.archive.org/web/20110623092608/http://www.ready.gov/america/beinformed/thunderstorms.html |archive-date=23 June 2011}} Preparing the home by removing dead or rotting limbs and trees, which can be blown over in high winds, can also significantly reduce the risk of property damage and personal injury.{{cite web|author=Federal Emergency Management Agency|title=What to Do Before a Thunderstorm|url=http://www.fema.gov/hazard/thunderstorm/th_before.shtm|publisher=US Department of Homeland Security|access-date=24 August 2011|url-status=dead|archive-url=https://web.archive.org/web/20110820113150/http://www.fema.gov/hazard/thunderstorm/th_before.shtm|archive-date=20 August 2011}}

The National Weather Service (NWS) in the United States recommends several precautions that people should take if thunderstorms are likely to occur:

:* Know the names of local counties, cities, and towns, as these are how warnings are described.

:* Monitor forecasts and weather conditions and know whether thunderstorms are likely in the area.{{cite web |url=http://www.lightningsafety.noaa.gov/blog.htm |title=NWS Lightning Safety Myths |publisher=Lightningsafety.noaa.gov |date=30 June 2014 |access-date=20 August 2014 |archive-date=28 March 2015 |archive-url=https://web.archive.org/web/20150328025002/http://www.lightningsafety.noaa.gov/blog.htm |url-status=dead }}

:* Be alert for natural signs of an approaching storm.

:* Cancel or reschedule outdoor events (to avoid being caught outdoors when a storm hits).

:* Take action early so you have time to get to a safe place.

:* Get inside a substantial building or hard-topped metal vehicle before threatening weather arrives.

:* If you hear thunder, get to the safe place immediately.

:* Avoid open areas like hilltops, fields, and beaches, and do not be or be near the tallest objects in an area when thunderstorms are occurring.

:* Do not shelter under tall or isolated trees during thunderstorms.

:* If in the woods, put as much distance as possible between you and any trees during thunderstorms.

:* If in a group, spread out to increase the chances of survivors who could come to the aid of any victims from a lightning strike.

While safety and preparedness often overlap, "thunderstorm safety" generally refers to what people should do during and after a storm. The American Red Cross recommends that people follow these precautions if a storm is imminent or in progress:

:* Take action immediately upon hearing thunder. Anyone close enough to the storm to hear thunder can be struck by lightning.

:* Avoid electrical appliances, including corded telephones. Cordless and wireless telephones are safe to use during a thunderstorm.

:* Close and stay away from windows and doors, as glass can become a serious hazard in high wind.

:* Do not bathe or shower, as plumbing conducts electricity.

:* If driving, safely exit the roadway, turn on hazard lights, and park. Remain in the vehicle and avoid touching metal.

The NWS stopped recommending the "lightning crouch" in 2008 as it does not provide a significant level of protection and will not significantly lower the risk of being killed or injured from a nearby lightning strike.{{cite web|url=http://www.srh.noaa.gov/jetstream/lightning/lightning_faq.htm#5 |title=NWS JetStream – Lightning Frequently Asked Questions |publisher=Srh.noaa.gov |date=28 June 2014 |access-date=20 August 2014}}{{cite news|url=http://www.latimes.com/nation/nationnow/la-na-nn-six-lightning-facts-20140714-htmlstory.html |title=You're not safer crouching: Six things you didn't know about lightning |newspaper=LA Times |access-date=20 August 2014}}

{{wide image|Thunderstorm near Cuero, Texas.jpg|1200 px|Thunderstorm near Cuero, Texas}}

{{See also|United States rainfall climatology}}

File:Interesting storm cloud in Oklahoma.jpg in Oklahoma]] Thunderstorms occur throughout the world, even in the polar regions, with the greatest frequency in tropical rainforest areas, where they may occur nearly daily. At any given time, approximately 2,000 thunderstorms are occurring on Earth.National Geographic Almanac of Geography, {{ISBN|0-7922-3877-X}}, page 75. Kampala and Tororo in Uganda have each been mentioned as the most thunderous places on Earth,{{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 | access-date = 23 August 2006 | url-status = dead | archive-url = https://web.archive.org/web/20070711070501/http://sky-fire.tv/index.cgi/thunderstorms.html#occur | archive-date = 11 July 2007 }} a claim also made for Singapore and Bogor on the Indonesian island of Java. Other cities known for frequent storm activity include Darwin, Caracas, Manila and Mumbai. Thunderstorms are associated with the various monsoon seasons around the globe, and they populate the rainbands of tropical cyclones.{{cite web|url=http://www.srh.noaa.gov/jetstream/tropics/tc_hazards.htm|title=Tropical Cyclone Hazards|access-date=30 August 2009|date=8 October 2008|author=National Weather Service JetStream|publisher=National Weather Service Southern Region Headquarters}} 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.{{cite web|author=David Roth|title=Unified Surface Analysis Manual|access-date=22 October 2006|publisher=Hydrometeorological Prediction Center|url= http://www.wpc.ncep.noaa.gov/sfc/UASfcManualVersion1.pdf}} 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.{{fact|date=May 2024}}

Some of the most powerful thunderstorms over the United States occur in the Midwest and the 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,{{cite web|url=http://www.ofcm.gov/slso/pdf/slsochp2.pdf |title=National Severe Local Storms Operations Plan – Chapter 2 |author=Office of the Federal Coordinator for Meteorology |publisher=Department of Commerce |date=7 June 2001 |access-date=23 August 2006 |url-status=dead |archive-url=https://web.archive.org/web/20090506002006/http://www.ofcm.gov/slso/pdf/slsochp2.pdf |archive-date=6 May 2009 }} but they occur with greater frequency in the inland areas, particularly the Sacramento and San Joaquin Valleys of California. In spring and summer, they occur nearly daily in certain areas of the Rocky Mountains as part of the North American Monsoon regime. In the Northeast, storms take on similar characteristics and patterns as the Midwest, but with less frequency and severity. During the summer, air-mass thunderstorms are an almost daily occurrence over central and southern parts of Florida.{{fact|date=May 2024}}

File:How thunderstorms launch particle beams into space 300dpi.jpg

{{See also|Sprite (lightning)|Upper-atmospheric lightning|St. Elmo's fire}}

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 a typical thunderstorm, approximately 5×10⁸ kg of water vapor are lifted, and the amount of energy released when this condenses is 10¹⁵ joules. This is on the same order of magnitude of energy released within a tropical cyclone, and more energy than that released during the atomic bomb blast at Hiroshima, Japan in 1945.{{failed verification|date=April 2024|reason=The source is a list of power values, none of which pertain to thunderstorm moisture or energy.}}

The Fermi Gamma-ray Burst Monitor results show that gamma rays and antimatter particles (positrons) can be generated in powerful thunderstorms.{{cite web|url=http://www.nasa.gov/mission_pages/GLAST/news/fermi-thunderstorms.html|title=Fermi Catches Antimatter-Hurling Storms|first=Rob|last=Garner|date=26 June 2015|work=nasa.gov|access-date=19 July 2016}} It is suggested that the antimatter positrons are formed in terrestrial gamma-ray flashes (TGF). TGFs are brief bursts occurring inside thunderstorms and associated with lightning. The streams of positrons and electrons collide higher in the atmosphere to generate more gamma rays.{{cite news|last=Ouellette|first=Jennifer|title=Fermi Spots Antimatter in Thunderstorms|url=http://news.discovery.com/space/fermi-spots-antimatter-in-thunderstorms.html|access-date=16 January 2011|newspaper=Discovery News|date=13 January 2011|archive-date=12 November 2012|archive-url=https://web.archive.org/web/20121112083132/http://news.discovery.com/space/fermi-spots-antimatter-in-thunderstorms.html|url-status=dead}} About 500 TGFs may occur every day worldwide, but mostly go undetected.

File:ChelmonskiJozef.1896.Burza.jpg – picture by Jozef Chelmonski, 1896, 107 cm (42.1 in)x163 cm (64.1 in), National Museum in Cracow]]

In more contemporary times, thunderstorms have taken on the role of a scientific curiosity. Every spring, storm chasers head to the Great Plains of the United States and the Canadian Prairies to explore the scientific aspects of storms and tornadoes through use of videotaping.{{cite web|url=http://www.cimms.ou.edu/~stumpf/cethics.html|title=Storm Chase Ethics|author=Alan Moller|author-link=Alan Moller|date=5 March 2003|access-date=9 September 2009}} Radio pulses produced by cosmic rays are being used to study how electric charges develop within thunderstorms.{{cite web|url=http://www.spaceref.com/news/viewpr.html?pid=28329|title=Scientists use high-energy particles from space to probe thunderstorms|date=2 June 2009|access-date=9 September 2009|author=Florida Institute of Technology|author-link=Florida Institute of Technology|archive-date=22 February 2023|archive-url=https://web.archive.org/web/20230222071727/https://spaceref.com/press-release/scientists-use-high-energy-particles-from-space-to-probe-thunderstorms/|url-status=dead}} More organized meteorological projects such as VORTEX2 use an array of sensors, such as the Doppler on Wheels, vehicles with mounted automated weather stations, weather balloons, and unmanned aircraft to investigate thunderstorms expected to produce severe weather.{{cite web|url=http://www.vortex2.org/home/|title=What is VORTEX2?|author=VORTEX2|date=2009|access-date=9 September 2009|archive-date=25 November 2020|archive-url=https://web.archive.org/web/20201125022823/http://vortex2.org/home/|url-status=dead}} Lightning is detected remotely using sensors that detect cloud-to-ground lightning strokes with 95 percent accuracy in detection and within {{convert|250|m|ft}} of their point of origin.{{cite web|url=http://ams.confex.com/ams/89annual/techprogram/paper_149149.htm|title=An Overview of the United States Precision Lightning Network (USPLN)|author=Peter P. Neilley|author2=R. B. Bent|name-list-style=amp|publisher=American Meteorological Society Fourth Conference on the Meteorological Applications of Lightning Data|date=2009|access-date=9 September 2009}}

Thunderstorms strongly influenced many early civilizations. Greeks believed that they were battles waged by Zeus, who hurled lightning bolts forged by Hephaestus. Some American Indian tribes associated thunderstorms with the Thunderbird, who they believed was a servant of the Great Spirit. The Norse considered thunderstorms to occur when Thor went to fight Jötnar, with the thunder and lightning being the effect of his strikes with the hammer Mjölnir. Hinduism recognizes Indra as the god of rain and thunderstorms. Christian doctrine accepts that fierce storms are the work of God. These ideas were still within the mainstream as late as the 18th century.{{cite book|author=John D. Cox|title=Storm Watchers|page=[https://archive.org/details/stormwatcherstur00cox_df1/page/7 7]|isbn=978-0-471-38108-2|date=2002|publisher=John Wiley & Sons, Inc.|url=https://archive.org/details/stormwatcherstur00cox_df1/page/7}}

Martin Luther was out walking when a thunderstorm began, causing him to pray to God for being saved and promising to become a monk.{{cite web|url=http://www.christianitytoday.com/history/people/theologians/martin-luther.html |title=Martin Luther|date=8 August 2008 |publisher=Christian History|language=en|access-date=6 July 2016}}

Thunderstorms, evidenced by flashes of lightning, on Jupiter have been detected and are associated with clouds where water may exist as both a liquid and ice, suggesting a mechanism similar to that on Earth. (Water is a polar molecule that can carry a charge, so it is capable of creating the charge separation needed to produce lightning).{{cite book

|first=Linda T.|last=Elkins-Tanton|date=2006

|title=Jupiter and Saturn|publisher=Chelsea House

|location=New York|isbn=978-0-8160-5196-0}} These electrical discharges can be up to a thousand times more powerful than lightning on the Earth.{{cite web

|editor = Watanabe, Susan

|date = 25 February 2006

|url = http://www.nasa.gov/vision/universe/solarsystem/galileo_end.html

|title = Surprising Jupiter: Busy Galileo spacecraft showed jovian system is full of surprises

|publisher = NASA

|access-date = 20 February 2007

|archive-date = 8 October 2011

|archive-url = https://web.archive.org/web/20111008010724/http://www.nasa.gov/vision/universe/solarsystem/galileo_end.html

|url-status = dead

}} The water clouds can form thunderstorms driven by the heat rising from the interior.{{cite journal

|last = Kerr|first = Richard A.

|title=Deep, Moist Heat Drives Jovian Weather

|journal=Science|date=2000|volume=287|issue=5455

|pages=946–947

|doi=10.1126/science.287.5455.946b

|s2cid = 129284864

}} The clouds of Venus may also be capable of producing lightning; some observations suggest that the lightning rate is at least half of that on Earth.{{cite journal|last=Russell|first=S. T.|date=2007|title=Lightning on Venus inferred from whistler-mode waves in the ionosphere|journal=Nature|volume=450|issue=7170|pages=661–662|bibcode=2007Natur.450..661R|doi=10.1038/nature05930|pmid=18046401|author2=Zhang, T.L.|author3=Delva, M.|s2cid=4418778|display-authors=etal}}

{{Portal|Weather}}

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{{Reflist|30em}}

• 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.
• {{cite journal | author = Davies J. M. | year = 2004 | title = Estimations of CIN and LFC associated with tornadic and nontornadic supercells | journal = Weather Forecast | volume = 19 | issue = 4| pages = 714–726 | doi = 10.1175/1520-0434(2004)019<0714:eocala>2.0.co;2 | bibcode = 2004WtFor..19..714D | doi-access = free }}
• 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.
• {{cite journal | last1= Doswell |first1=C.A. III |last2=Baker |first2=D. V. |last3=Liles |first3=C. A. | year = 2002 | title = Recognition of negative factors for severe weather potential: A case study | journal = Weather Forecast | volume = 17 | pages = 937–954 | doi = 10.1175/1520-0434(2002)017<0937:ronmff>2.0.co;2 | doi-access = free }}
• 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.
• Evans, Jeffry S.,: Examination of Derecho Environments Using Proximity Soundings. [http://www.spc.noaa.gov/publications/evans/bowpaper/bowpaper.htm NOAA.gov]
• J. V. Iribarne and W.L. Godson, Atmospheric Thermodynamics, published by D. Reidel Publishing Company, Dordrecht, the Netherlands, 1973
• M. K. Yau and R. R. Rogers, Short Course in Cloud Physics, Third Edition, published by Butterworth-Heinemann, 1 January 1989, {{ISBN|9780750632157}} {{ISBN|0-7506-3215-1}}

{{Commons category|Thunderstorms}}

{{Wikivoyage|Thunderstorms}}

• [http://www.canadiangeographic.ca/atlas/themes.aspx?id=weather&sub=weather_phenomena_thunderstorm&lang=En Anatomy of a thunderstorm] {{Webarchive|url=https://web.archive.org/web/20060218163706/http://www.canadiangeographic.ca/atlas/themes.aspx?id=weather&sub=weather_phenomena_thunderstorm&lang=En |date=18 February 2006 }}
• [http://www.ejssm.org/ Electronic Journal of Severe Storms Meteorology]

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