Editing Ice (section)

==== Hard forms ====
{{Further|Ice crystal}}
[[File:Granizo.jpg|right|thumb|A large hailstone, about {{convert|6|cm|in|abbr=on}} in diameter]]
[[Hail]] forms in storm [[cloud]]s when [[supercooled]] water droplets freeze on contact with [[condensation nuclei]], such as [[dust]] or [[dirt]]. The storm's [[updraft]] blows the hailstones to the upper part of the cloud. The updraft dissipates and the hailstones fall down, back into the updraft, and are lifted up again. 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|access-date=15 July 2009|author=Glossary of Meteorology|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20100725142407/http://amsglossary.allenpress.com/glossary/search?id=hail1|archive-date=25 July 2010}}</ref> Within [[METAR]] code, GR is used to indicate larger hail, of a diameter of at least {{convert|6.4|mm|in}} and GS for smaller.<ref name="METAR">{{cite web|url=http://www.alaska.faa.gov/fai/afss/metar+taf/sametara.htm|title=SA-METAR|author=Alaska Air Flight Service Station|publisher=[[Federal Aviation Administration]] via the Internet Wayback Machine|access-date=29 August 2009|date=10 April 2007|url-status=dead|archive-url=https://web.archive.org/web/20080501074014/http://www.alaska.faa.gov/fai/afss/metar%20taf/sametara.htm|archive-date=1 May 2008}}</ref> Stones of {{Convert|0.75|in|mm|order=flip}}, {{Convert|1.0|in|mm|order=flip}} and {{Convert|1.75|in|mm|order=flip}} are the most frequently reported hail sizes in North America.<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|author1=Jewell, Ryan|author2=Brimelow, Julian|date=17 August 2004|access-date=15 July 2009|url-status=live|archive-url=https://web.archive.org/web/20090507044027/http://www.spc.noaa.gov/publications/jewell/hailslsc.pdf|archive-date=7 May 2009}}</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=23 April 2007|access-date=15 July 2009|url-status=live|archive-url=https://web.archive.org/web/20090810182627/http://www.photolib.noaa.gov/htmls/nssl0001.htm|archive-date=10 August 2009}}</ref> In large hailstones, [[latent heat]] released by further freezing may melt the outer shell of the hailstone. The hailstone then may undergo 'wet growth', where the liquid outer shell collects other smaller hailstones.<ref>{{cite journal|title=Modeling Maximum Hail Size in Alberta Thunderstorms|journal=Weather and Forecasting|author1=Brimelow, Julian C. |author2=Reuter, Gerhard W. |author3=Poolman, Eugene R. |pages=1048–1062|volume=17|issue=5|doi=10.1175/1520-0434(2002)017<1048:MMHSIA>2.0.CO;2|bibcode = 2002WtFor..17.1048B|year=2002|doi-access=free}}</ref> The hailstone gains an ice layer and grows increasingly larger with each ascent. Once a hailstone becomes too heavy to be supported by the storm's updraft, it falls from the cloud.<ref>{{cite web|url=http://www.ucar.edu/communications/factsheets/Hail.html|title=Hail Fact Sheet|date=10 April 2000|author=Marshall, Jacque|access-date=15 July 2009|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}}</ref>
[[File:2013-02-23_03_59_28_Graupel_(snow_pellets)_in_Elko,_Nevada.JPG|thumb|right|Soft hail, or graupel, in [[Nevada]]]]
Hail forms in strong [[thunderstorm]] clouds, particularly those with intense updrafts, 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"/> Hail-producing clouds are often identifiable by their green coloration.<ref>{{cite web|url=http://www.abc.net.au/news/australia/qld/toowoomba/200410/s1222665.htm|archive-url=https://web.archive.org/web/20100306021712/http://www.abc.net.au/news/australia/qld/toowoomba/200410/s1222665.htm|archive-date=6 March 2010|title=Hail storms rock southern Qld|publisher=Australian Broadcasting Corporation|date=19 October 2004|access-date=15 July 2009}}</ref><ref>{{cite web|url=http://australiasevereweather.com/storm_news/arc1997.htm|title=Severe Thunderstorm Images of the Month Archives|year=1997|author1=Bath, Michael|author2=Degaura, Jimmy|access-date=15 July 2009|url-status=live|archive-url=http://archive.wikiwix.com/cache/20110713110215/http://australiasevereweather.com/storm_news/arc1997.htm|archive-date=13 July 2011}}</ref> The growth rate is maximized at about {{convert|-13|C|F|0}}, and becomes vanishingly small much below {{convert|-30|C|F|0}} as supercooled water droplets become rare. For this reason, 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>{{cite web|url=http://www.meted.ucar.edu/resource/soo/MesoAnalyst.htm|archive-url=https://web.archive.org/web/20030320222147/http://www.meted.ucar.edu/resource/soo/MesoAnalyst.htm|archive-date=20 March 2003|title=Meso-Analyst Severe Weather Guide|author=Wolf, Pete|date=16 January 2003|access-date=16 July 2009|publisher=University Corporation for Atmospheric Research}}</ref> [[Entrainment (meteorology)|Entrainment]] of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporative cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is actually 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 depth. Hail in the tropics occurs mainly at higher elevations.<ref>{{cite book|url=https://books.google.com/books?id=UbtG3vFfNtoC&pg=PA41|title=Climate, change and risk|author1=Downing, Thomas E. |author2=Olsthoorn, Alexander A. |author3=Tol, Richard S. J. |pages=41–43|publisher=Routledge|year=1999|isbn=978-0-415-17031-4}}</ref>
[[File:Sleet on the ground.jpg|thumb|An accumulation of ice pellets]]
Ice pellets ([[METAR]] code ''PL''<ref name="METAR"/>) are a form of precipitation consisting of small, [[translucent]] balls of ice, which are usually smaller than hailstones.<ref>{{cite web|url=http://www.weather.gov/glossary/index.php?word=hail|title=Hail (glossary entry)|publisher=National Oceanic and Atmospheric Administration's National Weather Service|access-date=20 March 2007|url-status=live|archive-url=https://web.archive.org/web/20071127004804/http://www.weather.gov/glossary/index.php?word=hail|archive-date=27 November 2007}}</ref> This form of precipitation is also referred to as "sleet" by the United States [[National Weather Service]].<ref>{{cite web|url=http://www.weather.gov/glossary/index.php?word=sleet|title=Sleet (glossary entry)|publisher=National Oceanic and Atmospheric Administration's National Weather Service|access-date=20 March 2007|url-status=live|archive-url=https://web.archive.org/web/20070218030309/http://www.weather.gov/glossary/index.php?word=sleet|archive-date=18 February 2007}}</ref> (In [[British English]] "sleet" refers to [[Rain and snow mixed|a mixture of rain and snow]].) Ice pellets typically form alongside freezing rain, when a wet [[warm front]] ends up between colder and drier atmospheric layers. There, raindrops would both freeze and shrink in size due to evaporative cooling.<ref>{{cite web|publisher=Weatherquestions.com|url=http://www.weatherquestions.com/What_causes_ice_pellets.htm|title=What causes ice pellets (sleet)?|access-date=8 December 2007|url-status=live|archive-url=https://web.archive.org/web/20071130071143/http://www.weatherquestions.com/What_causes_ice_pellets.htm|archive-date=30 November 2007}}</ref> So-called snow pellets, or [[graupel]], form when multiple water droplets freeze onto snowflakes until a soft ball-like shape is formed.<ref>{{cite web | url = https://sgil.ba.ars.usda.gov/snowsite/rimegraupel/rg.html | title = Rime and Graupel | website = [[U.S. Department of Agriculture]] Electron Microscopy Unit, Beltsville Agricultural Research Center | access-date = 2020-03-23 | archive-url = https://web.archive.org/web/20170711205706/https://sgil.ba.ars.usda.gov/snowsite/rimegraupel/rg.html | archive-date = 2017-07-11}}</ref> So-called "[[diamond dust]]", (METAR code ''IC''<ref name="METAR" />) also known as ice needles or ice crystals, forms at temperatures approaching {{convert|-40|C|F}} due to air with slightly higher moisture from aloft mixing with colder, surface-based air.<ref name="glossdia">{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=diamond+dust&submit=Search|title=Diamond Dust|author=Glossary of Meteorology|date=June 2000|publisher=American Meteorological Society|archive-url=https://web.archive.org/web/20090403084329/http://amsglossary.allenpress.com/glossary/search?p=1&query=diamond+dust&submit=Search|archive-date=3 April 2009|url-status=dead|access-date=21 January 2010}}</ref>