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| | The writer is called Wilber Pegues. One of the things she enjoys most is canoeing and she's been doing it for quite a whilst. My working day job is a travel agent. Some time ago he selected to live in North Carolina and he doesn't plan on altering it.<br><br>Feel free to visit my page; cheap psychic readings ([http://coachellavalleyvideos.com/users/MVarghese coachellavalleyvideos.com]) |
| [[File:Granizo.jpg|thumb|A large hailstone, about 6 cm (2.4 in) in diameter]]
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| {{Weather}}
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| '''Hail''' is a form of solid [[Precipitation (meteorology)|precipitation]]. It is often confused with, though distinct from, [[sleet]].<ref>http://www.straightdope.com/columns/read/1668/whats-the-difference-between-hail-sleet-and-freezing-rain</ref> It consists of balls or irregular lumps of ice, each of which is called a '''hailstone'''. Sleet falls generally in cold weather while hail growth is greatly inhibited at cold temperatures.<ref name="webster">{{cite web|title=Merriam-Webster definition of "hailstone"|publisher=[[Merriam-Webster]]|url=http://www.merriam-webster.com/dictionary/hailstone|accessdate=2013-01-23}}</ref> Unlike [[graupel]], which is made of [[hard rime|rime]], and [[ice pellets]], which are smaller and translucent, hailstones consist mostly of [[ice|water ice]] and measure between {{convert|5|mm|in|1}} and {{convert|15|cm|in|0}} in diameter. The [[METAR]] reporting code for hail {{convert|5|mm|in|abbr=on}} or greater is '''GR''', while smaller hailstones and graupel are coded '''GS'''. Hail is possible within most [[thunderstorm]]s as it is produced by [[cumulonimbus|cumulonimbi]],<ref name="gloss"/> and within {{convert|2|nmi|km}} of the parent storm. Hail formation requires environments of strong, upward motion of air with the parent thunderstorm (similar to [[tornado]]es) and lowered heights of the freezing level. In the [[mid-latitude]]s, hail forms near the [[continental climate|interiors of continents]], while in the [[tropics]], it tends to be confined to high [[elevation]]s.
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| There are methods available to detect hail-producing thunderstorms using [[weather satellite]]s and [[weather radar]] imagery. Hailstones generally fall at higher speeds as they grow in size, though complicating factors such as melting, friction with air, wind, and interaction with rain and other hailstones can slow their descent through [[Earth's atmosphere]]. Severe weather warnings are issued for hail when the stones reach a damaging size, as it can cause serious damage to human-made structures and, most commonly, farmers' crops.
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| == Definition ==
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| Any thunderstorm which produces hail that reaches the ground is known as a hailstorm.<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=Hailstorm|title=Hailstorm|author=Glossary of Meteorology|year=2009|accessdate=2009-08-29|publisher=[[American Meteorological Society]]}}</ref> Hail has a diameter of {{convert|5|mm|in}} or more.<ref name="gloss">{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=hail1|title=Hail|year=2009|accessdate=2009-07-15|author=Glossary of Meteorology|publisher=[[American Meteorological Society]]}}</ref> Hailstones can grow to {{convert|15|cm|in|0}} and weigh more than {{convert|0.5|kg|lb|1}}.<ref>{{cite web|url=http://www.photolib.noaa.gov/htmls/nssl0001.htm|title=Aggregate hailstone|author=National Severe Storms Laboratory|publisher=[[National Oceanic and Atmospheric Administration]]|date=2007-04-23|accessdate=2009-07-15}}</ref>
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| Unlike ice pellets, hailstones are layered and can be irregular and clumped together. Hail is composed of transparent ice or alternating layers of transparent and translucent ice at least {{convert|1|mm|in}} thick, which are deposited upon the hailstone as it travels through the cloud, suspended aloft by air with strong upward motion until its weight overcomes the [[vertical draft|updraft]] and falls to the ground. Although the diameter of hail is varied, in the United States, the average observation of damaging hail is between 2.5 cm (1 in) and [[golf ball]]-sized (1.75 in).<ref>{{cite web|url=http://www.spc.noaa.gov/publications/jewell/hailslsc.pdf|title=P9.5 Evaluation of an Alberta Hail Growth Model Using Severe Hail Proximity Soundings in the United States|author=Ryan Jewell and Julian Brimelow|date=2004-08-17|accessdate=2009-07-15}}</ref>
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| Stones larger than 2 cm (0.80 in) are usually considered large enough to cause damage. The [[Meteorological Service of Canada]] will issue severe thunderstorm warnings when hail that size or above is expected.<ref>{{Cite web|url=http://ec.gc.ca/meteo-weather/default.asp?lang=En&n=D9553AB5-1#severethunderstorm|title=Severe Thunderstorm criteria|author=Meteorological Service of Canada|publisher=[[Environment Canada]] | date= November 3, 2010|accessdate=2011-05-12}}</ref> The US [[National Weather Service]] has a 2.5 cm (1 in) or greater in diameter threshold, effective January 2010, an increase over the previous threshold of ¾-inch hail.<ref>{{Cite web|url=http://www.srh.noaa.gov/bmx/?n=oneinchhail|title=NEW 1 Inch Hail Criteria|author=National Weather Service|publisher=[[National Oceanic and Atmospheric Administration|NOAA]] | date= January 4, 2010 |accessdate=2011-05-12}}</ref> Other countries will have different thresholds according local sensitivity to hail; for instance grape growing areas could be adversely impacted by smaller hailstones. Hailstones can be very large or very small, depending on how strong the updraft is: weaker hailstorms produce smaller hailstones than stronger hailstorms (such as [[supercell]]s).
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| == Formation ==
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| Hail forms in strong [[thunderstorm]] clouds, particularly those with intense [[updraft]]s, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing {{convert|0|C|F|0}}.<ref name="gloss"/> These types of strong updrafts can also indicate the presence of a tornado.<ref>{{cite web|url=http://www.erh.noaa.gov/cae/svrwx/hail.htm|title=Hail...|accessdate=2009-08-28|date=2009-01-27|author=[[National Weather Service]] Forecast Office, [[Columbia, South Carolina]]|publisher=[[National Weather Service]] Eastern Region Headquarters}}</ref>
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| The growth rate is maximized where air is near a temperature of {{convert|-13|C|F|0}}.{{Citation needed|date=August 2012}}
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| === Layer nature of the hailstones ===
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| [[File:hailshaft.jpg|thumb|right|Hail shaft]]
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| [[File:Hail clouds.jpg|thumb|Severe thunderstorms containing hail can exhibit a characteristic green coloration<ref>{{cite journal|journal=Journal of Applied Meteorology|page=1754|author=Frank W. Gallagher, III.|title=Distant Green Thunderstorms – Frazer's Theory Revisited|volume=39|date=October 2000|publisher=[[American Meteorological Society]]|doi=10.1175/1520-0450-39.10.1754|issue=10|bibcode = 2000JApMe..39.1754G }}</ref>]]
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| Like other precipitation in cumulonimbus clouds hail begins as water droplets. As the droplets rise and the temperature goes below freezing, they become [[supercooled]] [[water]] and will freeze on contact with [[condensation nuclei]]. A cross-section through a large hailstone shows an onion-like structure. This means the hailstone is made of thick and translucent layers, alternating with layers that are thin, white and opaque. Former theory suggested that hailstones were subjected to multiple descents and ascents, falling into a zone of humidity and refreezing as they were uplifted. This up and down motion was thought to be responsible for the successive layers of the hailstone. New research, based on theory as well as field study, has shown this is not necessarily true.
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| The storm's [[updraft]], with upwardly directed wind speeds as high as {{convert|110|mph|km/h}},<ref name="ncar">{{cite web|url=http://www.ncar.ucar.edu/research/meteorology/storms/hail.php|title=Hail|year=2008|accessdate=2009-07-18|author=National Center for Atmospheric Research|publisher=University Corporation for Atmospheric Research}}</ref> blows the forming hailstones up the cloud. As the hailstone ascends it passes into areas of the cloud where the concentration of humidity and supercooled water droplets varies. The hailstone’s growth rate changes depending on the variation in humidity and supercooled water droplets that it encounters. The accretion rate of these water droplets is another factor in the hailstone’s growth. When the hailstone moves into an area with a high concentration of water droplets, it captures the latter and acquires a translucent layer. Should the hailstone move into an area where mostly water vapour is available, it acquires a layer of opaque white ice.<ref name=Nelson/>
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| Furthermore, the hailstone’s speed depends on its position in the cloud’s updraft and its mass. This determines the varying thicknesses of the layers of the hailstone. The accretion rate of supercooled water droplets onto the hailstone depends on the relative velocities between these water droplets and the hailstone itself. This means that generally the larger hailstones will form some distance from the stronger updraft where they can pass more time growing.<ref name=Nelson/> As the hailstone grows it releases [[latent heat]], which keeps its exterior in a liquid phase. Because it undergoes 'wet growth', the outer layer is ''sticky'', or more adhesive, so a single hailstone may grow by collision with other smaller hailstones, forming a larger entity with an irregular shape.<ref name="Brimlow">{{cite journal|title=Modeling Maximum Hail Size in Alberta Thunderstorms|journal=Weather and Forecasting|author=Julian C. Brimelow, Gerhard W. Reuter, and Eugene R. Poolman|date=October 2002|pages=1048–1062|volume=17|issue=5|doi=10.1175/1520-0434(2002)017<1048:MMHSIA>2.0.CO;2|issn=1520-0434|year=2002|bibcode=2002WtFor..17.1048B}}</ref>
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| The hailstone will keep rising in the thunderstorm until its mass can no longer be supported by the updraft. This may take at least 30 minutes based on the force of the updrafts in the hail-producing thunderstorm, whose top is usually greater than 10 km high. It then falls toward the ground while continuing to grow, based on the same processes, until it leaves the cloud. It will later begin to melt as it passes into air above freezing temperature.<ref>{{cite web|url=http://www.ucar.edu/communications/factsheets/Hail.html|title=Hail Fact Sheet|date=2000-04-10|author=Jacque Marshall|accessdate=2009-07-15|publisher=[[University Corporation for Atmospheric Research]]}}</ref>
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| Thus, a unique trajectory in the thunderstorm is sufficient to explain the layer-like structure of the hailstone. The only case in which multiple trajectories can be discussed is in a multicellular thunderstorm, where the hailstone may be ejected from the top of the "mother" cell and captured in the updraft of a more intense "daughter" cell. This, however, is an exceptional case.<ref name="Nelson">{{cite journal|title=The Influence of Storm Flow Struce on Hail Growth|journal=Journal of Atmospheric Sciences |author=Stephan P. Nelson|month= August|pages=1965–1983|volume=40|issue=8|doi=10.1175/1520-0469(1983)040<1965:TIOSFS>2.0.CO;2 |issn=1520-0469 |year=1983 |bibcode = 1983JAtS...40.1965N }}</ref>
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| === Factors favoring hail ===
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| Hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of {{convert|11000|ft|m}}.<ref name="mesoanal">{{cite web|url=http://www.meted.ucar.edu/resource/soo/MesoAnalyst.htm|title=Meso-Analyst Severe Weather Guide|first=Pete |last=Wolf|date=2003-01-16|accessdate=2009-07-16|publisher=[[University Corporation for Atmospheric Research]]}}</ref> [[Entrainment (meteorology)|Movement]] of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporational cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is less common in the tropics despite a much higher frequency of thunderstorms than in the mid-latitudes because the atmosphere over the tropics tends to be warmer over a much greater altitude. Hail in the tropics occurs mainly at higher elevations.<ref>{{cite book| author = Thomas E. Downing, Alexander A. Olsthoorn, Richard S. J. Tol| title = Climate, change and risk| url = http://books.google.com/?id=UbtG3vFfNtoC| accessdate = 2009-07-16| year = 1999| publisher = Routledge| isbn = 978-0-415-17031-4| pages = 41–43 }}</ref>
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| Hail growth becomes vanishingly small when air temperatures fall below {{convert|-30|C|F|0}} as supercooled water droplets become rare at these temperatures.<ref name="mesoanal"/> Around thunderstorms, hail is most likely within the cloud at elevations above {{convert|20000|ft|m}}. Between {{convert|10000|ft|m}} and {{convert|20000|ft|m}}, 60 percent of hail is still within the thunderstorm, though 40 percent now lies within the clear air under the anvil. Below {{convert|10000|ft|m}}, hail is equally distributed in and around a thunderstorm to a distance of {{convert|2|nmi|km}}.<ref>{{cite web|url=http://www.skybrary.aero/bookshelf/books/163.pdf|title=Flight Briefing Notes: Adverse Weather Operations Optimum Use of Weather Radar|page=2|author=[[Airbus]]|publisher=SKYbrary|date=2007-03-14|accessdate=2009-11-19}}</ref>
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| == Climatology ==
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| Hail occurs most frequently within continental interiors at mid-latitudes and is less common in the tropics, despite a much higher frequency of thunderstorms than in the mid-latitudes.<ref>{{cite journal|doi=10.1002/met.236|date=January 2011|title=A global hail climatology using the UK Met Office convection diagnosis procedure (CDP) and model analyses|author=W.H. Hand and G. Cappelluti|publisher=Meteorological Applications. Wiley|journal=Meteorological Applications|volume=18|issue=4|pages=446|bibcode = 2011MeApp..18..446H }}</ref> Hail is also much more common along mountain ranges because mountains force horizontal winds upwards (known as [[orographic lift]]ing), thereby intensifying the updrafts within thunderstorms and making hail more likely.<ref>{{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|accessdate=2009-08-28|date=2007-09-04|archiveurl=http://web.archive.org/web/20090621231613/http://www.ga.gov.au/hazards/severeweather/where.jsp <!--Added by H3llBot-->|archivedate=2009-06-21}}</ref> The higher elevations also result in there being less time available for hail to melt before reaching the ground. 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.<ref name="Oliver">{{cite book| author = John E. Oliver| title = Encyclopedia of World Climatology| url = http://books.google.com/?id=-mwbAsxpRr0C| accessdate = 2009-08-28| year = 2005| publisher = Springer| isbn = 978-1-4020-3264-6| page = 401 }}</ref> [[China]] also experiences significant hailstorms.<ref>{{cite journal|title=The characteristics of cloud-to-ground lightning activity in hailstorms over northern China |author=Dongxia Liu, Guili Feng, and Shujun Wu|date=February 2009|journal=Atmospheric Research|volume=91|issue=2–4|pages=459–465|doi=10.1016/j.atmosres.2008.06.016}}</ref> Central Europe and southern Australia also experience a lot of hailstorms. Popular regions for hailstorms are southern and western [[Germany]], northern and eastern [[France]] and southern and eastern [[Benelux]]. In south-eastern Europe, [[Croatia]] and [[Serbia]] experience frequent occurrences of hail.<ref>{{cite journal|title=Hail characteristics of different regions in continental part of Croatia based on influence of orography|author=Damir Počakal, Željko Večenaj, and Janez Štalec|journal=Atmospheric Research|volume=93|issue=1–3|date=July 2009|doi=10.1016/j.atmosres.2008.10.017|pages=516}}</ref>
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| In [[North America]], hail is most common in the area where [[Colorado]], [[Nebraska]], and [[Wyoming]] meet, known as "Hail Alley".<ref name="ncarhail">{{cite web|url=http://www.ucar.edu/communications/factsheets/Hail.html|title=Fact Sheet on Hail|accessdate=2009-07-18|author=Rene Munoz|date=2000-06-02|publisher=University Corporation for Atmospheric Research}}</ref> 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.<ref name="Nolanhail"/>
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| == Short-term detection ==
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| [[File:Three body scatter spike-NOAA.png|thumb|Example of a three body spike: the weak triangular echoes (pointed by the arrow) behind the red and white thunderstorm core are related to hail inside the storm.]]
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| [[Weather radar]] is a very useful tool to detect the presence of hail-producing thunderstorms. However, radar data has to be complemented by a knowledge of current atmospheric conditions which can allow one to determine if the current atmosphere is conducive to hail development.
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| Modern radar scans many angles around the site. Reflectivity values at multiple angles above ground level in a storm are proportional to the precipitation rate at those levels. Summing reflectivities in the [[Vertically Integrated Liquid]] or VIL, gives the [[liquid water content]] in the cloud. Research shows that hail development in the upper levels of the storm is related to the evolution of VIL. VIL divided by the vertical extent of the storm, called VIL density, has a relationship with hail size, although this varies with atmospheric conditions and therefore is not highly accurate.<ref>{{cite web|url=http://www.srh.noaa.gov/hgx/projects/hail_study.htm|title=VIL density and Associated Hail Size Along the Northwest Gulf Coast|author=Charles A. Roeseler and Lance Wood|publisher=[[National Weather Service]] Southern Region Headquarters|date=2006-02-02|accessdate=2009-08-28|archiveurl = http://web.archive.org/web/20070818231127/http://www.srh.noaa.gov/hgx/projects/hail_study.htm |archivedate = August 18, 2007|deadurl=yes}}</ref> Traditionally, hail size and probability can be estimated from radar data by computer using algorithms based on this research. Some algorithms include the height of the freezing level to estimate the melting of the hailstone and what would be left on the ground.
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| Certain patterns of reflectivity are important clues for the meteorologist as well. The [[three body scatter spike]] is an example. This is the result of energy from the radar hitting hail and being deflected to the ground, where they deflect back to the hail and then to the radar. The energy took more time to go from the hail to the ground and back, as opposed to the energy that went direct from the hail to the radar, and the echo is further away from the radar than the actual location of the hail on the same radial path, forming a cone of weaker reflectivities.
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| More recently, the [[Weather radar#Polarization|polarization]] properties of weather radar returns have been analyzed to differentiate between hail and heavy rain.<ref>{{cite journal |first1=K. |last1=Aydin |first2=T.A. |last2=Seliga |first3=V. |last3=Balaji |date=October 1986 |title=Remote Sensing of Hail with a Dual Linear Polarization Radar |journal=Journal of Climate and Applied Meteorology |volume=25 |issue=10 |pages=1475–14 |doi=10.1175/1520-0450(1986)025<1475:RSOHWA>2.0.CO;2 |issn=1520-0450|bibcode = 1986JApMe..25.1475A }}</ref><ref>{{cite web|url=http://www.chill.colostate.edu/w/Hail_signature_development|title=Hail Signature Development|author=[[Colorado State University]]-CHILL National Radar Facility|publisher=[[Colorado State University]]|date=2007-08-22|accessdate=2009-08-28}}</ref> The use of differential reflectivity (<math>Z_{dr}</math>), in combination with horizontal reflectivity (<math>Z_{h}</math>) has led to a variety of hail classification algorithms.<ref>{{cite web|url=http://www.chill.colostate.edu/w/Hydrometeor_classification_example|title=Hydrometeor classification example|author=[[Colorado State University]]-CHILL National Radar Facility|publisher=[[Colorado State University]]|date=2008-08-25|accessdate=2009-08-28}}</ref> Visible satellite imagery is beginning to be used to detect hail, but false alarm rates remain high using this method.<ref>{{cite journal|doi=10.1016/S0169-8095(96)00032-4|date=1998-07-25|title=Satellite data based detection and prediction of hail|last1=Bauer-Messmer|first1=Bettina|last2=Waldvogel|first2=Albert|journal=Atmospheric Research|volume=43|issue=3|pages=217}}</ref>
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| == Size and terminal velocity ==
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| [[File:Hailstones.jpg|right|thumb|210px|right|Hailstones ranging in size from few millimetres to over a centimetre in diameter.]]
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| [[File:Hagelkorn mit Anlagerungsschichten.jpg|thumb|right|275px|Large hailstone with concentric rings]]
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| The size of hailstones is best determined by measuring their diameter with a ruler. In the absence of a ruler, hailstone size is often visually estimated by comparing its size to that of known objects, such as coins.<ref>{{cite web|url=http://dnrdata.dnr.ne.gov/NeRAIN/docs/hail.asp|title=NeRAIN Data Site-Measuring Hail|author=Nebraska Rainfall Assessment and Information Network|publisher=Nebraska Department of Natural Resources|year=2009|accessdate=2009-08-29}}</ref> Using the objects such as hen's eggs, peas, and marbles for comparing hailstone sizes is often imprecise, due to their varied dimensions. The UK organisation, [[TORRO]], also scales for both hailstones and hailstorms.<ref>{{cite web|url=http://www.torro.org.uk/torro/severeweather/hailscale.php|title=Hail Scale|author=The TORnado and storm Research Organization|accessdate=2009-08-28|year=2009}}</ref> When observed at an [[airport]], [[METAR]] code is used within a [[surface weather observation]] which relates to the size of the hailstone. Within METAR code, GR is used to indicate larger hail, of a diameter of at least {{convert|0.25|in|mm}}. GR is derived from the French word grêle. Smaller-sized hail, as well as snow pellets, use the coding of GS, which is short for the French word grésil.<ref>{{cite web|url=http://www.alaska.faa.gov/fai/afss/metar%20taf/sametara.htm|title=SA-METAR|author=Alaska Air Flight Service Station|publisher=[[Federal Aviation Administration]]|accessdate=2009-08-29|date=2007-04-10|archiveurl = http://web.archive.org/web/20080501074014/http://www.alaska.faa.gov/fai/afss/metar%20taf/sametara.htm |archivedate = May 1, 2008|deadurl=yes}}</ref>
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| [[File:Record hailstone Vivian, SD.jpg|thumb|right|237px|The largest recorded hailstone in the United States by diameter {{convert|8|in|cm}} and weight {{convert|1.93|lb|kg}}. The hailstone fell in Vivian, South Dakota on July 23, 2010.]]
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| ===Hail records===
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| [[Megacryometeors]], large rocks of ice that are not associated with thunderstorms, are not officially recognized by the [[World Meteorological Organization]] as "hail," which are aggregations of ice associated with thunderstorms, and therefore records of extreme characteristics of megacryometers are not given as hail records.
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| * '''Heaviest:''' 1.0 kg (2.25 lb); [[Gopalganj District (Bangladesh)|Gopalganj District]], Bangladesh, 14 April 1986.<ref name="weather extremes">{{cite web|url=http://www.wrh.noaa.gov/sgx/research/Guide/weatherextremes.pdf| title=Appendix I – Weather Extremes| publisher =[[National Weather Service]] | location=San Diego, California| archiveurl =http://web.archive.org/web/20080528065516/http://www.wrh.noaa.gov/sgx/research/Guide/weatherextremes.pdf| archivedate =28 May 2008| accessdate =2010-06-01}}</ref>
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| * '''Largest diameter officially measured:''' {{convert|8.0|in|cm}} [[diameter]], {{convert|18.625|in|cm|sigfig=3}} [[circumference]]; [[Vivian, South Dakota]], 23 July 2010.<ref>{{cite web| url = http://www.crh.noaa.gov/abr/?n=stormdamagetemplate| title = Record Setting Hail Event in Vivian, South Dakota on July 23, 2010| author = NWS| date = 30 July 2010| publisher = National Weather Service| location = [[Aberdeen, South Dakota]]| archiveurl = http://www.webcitation.org/5rhd1coDR| archivedate = 3 August 2010| accessdate = 2010-08-03}}</ref>
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| * '''Largest circumference officially measured:''' {{convert|18.75|in|cm|sigfig=3}} circumference, {{convert|7.0|in|cm}} diameter; [[Aurora, Nebraska]], 22 June 2003.<ref name="weather extremes"/><ref name="NG Hail">{{cite web|url=http://news.nationalgeographic.com/news/2003/08/0804_030804_largesthailstone.html |title=Largest Hailstone in U.S. History Found |publisher=News.nationalgeographic.com |accessdate=2010-08-20}}</ref>
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| [[Terminal velocity]] of hail, or the speed at which hail is falling when it strikes the ground, varies by the [[diameter]] of the hailstones. A hailstone of {{convert|1|cm|in}} in diameter falls at a rate of {{convert|9|m/s|mph}}, while stones the size of {{convert|8|cm|in}} in diameter fall at a rate of {{convert|48|m/s|mph}}. Hailstone velocity is dependent on the size of the stone, friction with air it is falling through, the motion of [[wind]] it is falling through, collisions with raindrops or other hailstones, and melting as the stones fall through a warmer [[atmosphere]].<ref>{{cite web|url=http://www.nssl.noaa.gov/primer/hail/hail_basics.html|title=Hail Basics|author=[[National Severe Storms Laboratory]]|publisher=[[National Oceanic and Atmospheric Administration]]|date=2006-11-15|accessdate=2009-08-28}}</ref>
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| == Hazards ==
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| {{Main|List of costly or deadly hailstorms}}
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| Hail can cause serious damage, notably to [[automobile]]s, aircraft, skylights, glass-roofed structures, [[livestock]], and most commonly, farmers' [[crops]].<ref name="Nolanhail">{{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|accessdate=2009-07-18}}</ref> Hail damage to roofs often goes unnoticed until further structural damage is seen, such as leaks or cracks. It is hardest to recognize hail damage on shingled roofs and flat roofs, but all roofs have their own hail damage detection problems.<ref name="Adjusting Today">{{cite web |url= http://www.adjustersinternational.com/AdjustingToday/ATfullinfo.cfm?start=16&page_no=16&pdfID=16|title= Hail Damage to Roofs |accessdate= 2009-12-11 |publisher= Adjusting Today }}</ref> Metal roofs are fairly resistant to hail damage, but may accumulate cosmetic damage in the form of dents and damaged coatings.<ref>{{Cite web
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| |url=http://www.infinityroofer.com/metal-roofing
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| |title=Metal Roofing
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| }}</ref>
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| Hail is one of the most significant thunderstorm hazards to aircraft.<ref>{{cite web|url=http://www.easa.europa.eu/safety-and-research/research-projects/docs/large-aeroplanes/EASA.2008_5.pdf|date=November 2010|title=Hail Threat Standardisation|author=P.R. Field, W.H. Hand, G. Cappelluti et al.|publisher=European Aviation Safety Agency. RP EASA.2008/5}}</ref> When hailstones exceed {{convert|0.5|in|mm}} in diameter, planes can be seriously damaged within seconds.<ref>{{cite web|url=http://www.aviationweather.ws/063_Hazards.php|title=Hazards|author=[[Federal Aviation Administration]]|year=2009|accessdate=2009-08-29}}</ref> The hailstones accumulating on the ground can also be hazardous to landing aircraft. Hail is also a common nuisance to drivers of automobiles, severely denting the vehicle and cracking or even shattering [[windshields]] and [[Car glass|windows]]. Wheat, corn, soybeans, and tobacco are the most sensitive crops to hail damage.<ref name="Oliver"/> Hail is one of Canada's most expensive hazards.<ref>{{cite book| author = Damon P. Coppola| title = Introduction to international disaster management| url = http://books.google.com/?id=s6oxEraqWWwC| year = 2007| publisher = Butterworth-Heinemann| isbn = 978-0-7506-7982-4| page = 62 }}</ref> Rarely, massive hailstones have been known to cause [[concussion]]s or fatal head [[physical trauma|trauma]]. 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]].<ref>{{cite web|url=http://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=2004-11-07|accessdate=2009-08-28|publisher=Telegraph Group Unlimited via the Internet Wayback Machine |archiveurl = http://web.archive.org/web/20051203015218/http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2004/11/07/wind07.xml&sSheet=/news/2004/11/07/ixworld.html |archivedate = 2005-12-03}}</ref> The largest hailstone in terms of diameter and weight ever recorded in the [[United States]] fell on July 23, 2010 in [[Vivian, South Dakota]]; it measured {{convert|8|in|cm}} in diameter and {{convert|18.62|in|cm}} in circumference, weighing in at {{convert|1.93|lbs|kg}}.<ref name="Record">{{cite web|title=Hailstone record press release|date=2010-07-30|publisher=National Weather Service|url=http://www.crh.noaa.gov/crh/pdf/073010RecordHailVivianSD.pdf}}</ref> This broke the previous record for diameter set by a hailstone 7 inches diameter and 18.75 inches circumference (still the greatest ''circumference'' hailstone) which fell in [[Aurora, Nebraska]] in the United States on June 22, 2003, as well as the record for weight, set by a hailstone of {{convert|1.67|lbs|kg}} that fell in [[Coffeyville, Kansas]] in 1970.<ref name="Record"/>
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| == Accumulations ==
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| Narrow zones where hail accumulates on the ground in association with thunderstorm activity are known as hail streaks or hail swaths,<ref>{{cite web|url=http://www.nssl.noaa.gov/primer/hail/hail_climatology.html|title=Hail Climatology|author=National Severe Storms Laboratory|publisher=[[National Oceanic and Atmospheric Administration]]|date=2006-10-09|accessdate=2009-08-29}}</ref> which can be detectable by satellite after the storms pass by.<ref>{{cite web|url=http://www-roc.inria.fr/clime/lynx/peters-factsheet.pdf|title=Crop Hail Damage Assessment|author=Albert J. Peters|publisher=Institut National De Recherche En Informatique Et En Automatique|date=2003-03-03|accessdate=2009-08-28}}</ref> Hailstorms normally last from a few minutes up to 15 minutes in duration.<ref name="Nolanhail"/> Accumulating hail storms can blanket the ground with over {{convert|2|in|cm}} of hail, cause thousands to lose power, and bring down many trees. Flash flooding and mudslides within areas of steep terrain can be a concern with accumulating hail.<ref>{{cite news|url=http://www.thesudburystar.com/ArticleDisplay.aspx?e=1612615|title=Sudbury lashed by freak storm; hail pummels downtown core|author=Harold Carmichael|date=2009-06-15|accessdate=2009-08-28|paper=Sudbury Star|publisher=Sun Media}}</ref>
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| On somewhat rare occasions, a thunderstorm can become stationary or nearly so while prolifically producing hail and significant depths of accumulation do occur; this tends to happen in mountainous areas, such as the July 29, 2010 case<ref>http://www.coloradodaily.com/rant-rave/ci_15630529#axzz1NnYBPl6D</ref> of a foot of hail accumulation in [[Boulder County]], Colorado. Depths of up to a metre have been reported. A landscape covered in accumulated hail generally resembles one covered in accumulated snow and any significant accumulation of hail has the same restrictive effects as snow accumulation, albeit over a smaller area, on transport and infrastructure. Accumulated hail can also cause flooding by blocking drains, and hail can be carried in the floodwater, turning into a snow-like slush which is deposited at lower elevations.
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| == Suppression and prevention ==
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| During the [[Middle Ages]], people in Europe used to ring church bells and fire [[cannon]]s to try to prevent hail, and the subsequent damage to crops. Updated versions of this approach are available as modern [[hail cannon]]s. [[Cloud seeding]] after [[World War II]] was done to eliminate the hail threat,<ref name="ncar"/> particularly across [[Russia]] – where it was claimed a 50 to 80 percent reduction in crop damage from hail storms was achieved by deploying [[silver iodide]] in clouds using [[rocket]]s and [[artillery shell]]s. Their results have not been verified. Hail suppression programs have been undertaken by 15 countries between 1965 and 2005.<ref name="Oliver"/> To this day, no hail prevention method has been proven to work.<ref name="ncar"/>
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| == See also ==
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| * [[Graupel]]
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| * [[Ice pellets]]
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| * [[Megacryometeor]]
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| * [[Sleet (disambiguation)]]
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| == References ==
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| {{Reflist|30em}}
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| == Further reading ==
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| * {{cite book| last = Rogers and Yau| title = A Short Course in CLOUD PHYSICS| year = 1989| publisher = Butterworth-Heinemann| location = Massachusetts| isbn = 0-7506-3215-1 }}
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| * {{cite book| last = Jim Mezzanotte| title = Hailstorms| year = 2007| publisher = Gareth Stevens Publishing| isbn = 978-0-8368-7912-4 }}
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| * {{cite book| last = Snowden Dwight Flora| title = Hailstorms of the United States| year = 2003| publisher = Textbook Publishers| isbn = 978-0-7581-1698-7 }}
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| * {{cite book | last = Narayan R. Gokhale | title = Hailstorms and Hailstone Growth | publisher = State University of New York Press | year = 1974 | isbn = 978-0-87395-313-9 }}
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| * {{cite book| last = Duncan Scheff| title = Ice and Hailstorms| year = 2001| publisher = Raintree Publishers| isbn = 978-0-7398-4703-9 }}
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| == External links ==
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| {{Commons category|Hail}}
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| {{Wiktionary|Hail|hail}}
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| {{AmCyc Poster|Hail}}
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| * [http://www.hailtrends.com Hail Storm Research Tools]
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| * [http://www.hail.org Hail by income and population (Realtime)]
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| * [http://www.ucar.edu/communications/factsheets/Hail.html Hail Factsheet]
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| * [http://www.economics.noaa.gov/?goal=weather&file=events/hail/ The Economic Costs of Hail Storm Damage] NOAA Economics
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| ; Images
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| * [http://www.chaseday.com/hail.htm Hail and hailstorms]
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| * [http://www.metsul.com/secoes/visualiza.php?cod_subsecao=28&cod_texto=956 Major hail event in Brazil]
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| * [http://hail.org/map/NOAA.html NOAA Hail Reports on Google map (non commercial)]
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| ; Video
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| * [http://www.youtube.com/watch?v=RLKabmwVGqs Major Hail Storm in Calgary, Alberta, Canada, Aug.22,2010]
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| {{Natural disasters}}
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| {{good article}}
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| [[Category:Precipitation]]
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| [[Category:Snow or ice weather phenomena]]
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| [[Category:Storm]]
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| [[Category:Weather hazards]]
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| {{Link GA|pt}}
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