View source for Snow

{{short description|Precipitation in the form of ice crystal flakes}}
{{Other uses}}
{{Redirect|Snowfall}}
{{pp-move}}
{{pp-vandalism|small=yes}}
{{Infobox material
| name = Snow
| image = CargoNet Di 12 Euro 4000 Lønsdal - Bolna.jpg
| alt =
| caption = [[Norway|Norwegian]] train plowing through drifted snow
| type =
| density = 0.1–0.8 g/cm<sup>3</sup>
| radiation_resistance =
| uv_resistance =
| youngs_modulus =
| tensile_strength = 1.5–3.5 kPa<ref name = Snowenclyclopedia/>
| elongation =
| compressive_strength = 3–7 MPa<ref name = Snowenclyclopedia/>
| poissons_ratio =
| coeff_friction =
| melting_point = 0 °C
| heat_transfer_coeff =
| thermal_conductivity_note = For densities 0.1 to 0.5 g/cm<sup>3</sup><!---http://www.the-cryosphere.net/7/217/2013/tc-7-217-2013.pdf--->
| thermal_conductivity = 0.05–0.7 W/(K·m)
| thermal_diffusivity_note =
| thermal_diffusivity =
| linear_expansion =
| specific_heat =
| dielectric_constant_note = For dry snow density 0.1 to 0.9 g/cm<sup>3</sup><!----http://www.dtic.mil/dtic/tr/fulltext/u2/p000148.pdf---->
| dielectric_constant = 1–3.2
| footnotes = The physical properties of snow vary considerably from event to event, sample to sample, and over time.
|image_size=300px}}

{{Use mdy dates|date=December 2016}}

{{Weather}}

'''Snow''' consists of individual [[ice]] crystals that grow while suspended in the [[atmosphere]]—usually within clouds—and then fall, accumulating on the ground where they undergo further changes.<ref name="Hobbs">
{{cite book
 | last = Hobbs
 | first = Peter V.
 | title = Ice Physics
 | publisher = Oxford University Press
 | date = 2010
 | location = Oxford
 | pages = 856
 | isbn = 978-0199587711 }}</ref> It consists of frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size, precipitate and accumulate on surfaces, then metamorphose in place, and ultimately melt, slide, or [[Sublimation (phase transition)|sublimate]] away.

[[Snowstorm]]s organize and develop by feeding on sources of atmospheric moisture and cold air. [[Snowflake]]s [[Nucleation|nucleate]] around particles in the atmosphere by attracting [[supercooling|supercooled]] water droplets, which [[Freezing|freeze]] in hexagonal-shaped crystals. Snowflakes take on a variety of shapes, basic among these are platelets, needles, columns, and [[Hard rime|rime]]. As snow accumulates into a [[snowpack]], it may blow into drifts. Over time, accumulated snow metamorphoses, by [[sintering]], [[sublimation (phase transition)|sublimation]], and [[freeze-thaw]]. Where the climate is cold enough for year-to-year accumulation, a [[glacier]] may form. Otherwise, snow typically melts seasonally, causing runoff into streams and rivers and recharging [[groundwater]].

Major snow-prone areas include the [[Polar regions of Earth|polar regions]], the northernmost half of the [[Northern Hemisphere]], and mountainous regions worldwide with sufficient moisture and cold temperatures. In the [[Southern Hemisphere]], snow is confined primarily to mountainous areas, apart from [[Antarctica]].<ref>
{{cite book
 |last        = Rees
 |first       = W. Gareth
 |title       = Remote Sensing of Snow and Ice
 |publisher   = CRC Press
 |date        = 2005
 |pages       = 312
 |isbn        = 978-1-4200-2374-9
 |url         = https://books.google.com/books?id=780IKxPcqpYC&pg=PA2
 }}</ref>

Snow affects such human activities as [[transportation]]: creating the need for keeping roadways, wings, and windows clear; [[agriculture]]: providing water to crops and safeguarding livestock; [[sport]]s such as [[skiing]], [[snowboarding]], and [[Snowmobile|snowmachine]] travel; and [[warfare]]. Snow affects [[ecosystem]]s, as well, by providing an insulating layer during winter under which plants and animals are able to survive the cold.<ref name=Snowenclyclopedia>{{Citation
 |author           = Michael P. Bishop
 |author2          = Helgi Björnsson
 |author3          = Wilfried Haeberli
 |author4          = Johannes Oerlemans
 |author5          = John F. Shroder
 |author6          = Martyn Tranter
 |editor-last      = Singh
 |editor-first     = Vijay P.
 |editor2-last     = Singh
 |editor2-first    = Pratap
 |editor3-last     = Haritashya
 |editor3-first    = Umesh K.
 |year             = 2011
 |pages            = 1253
 |isbn             = 978-90-481-2641-5
 |title            = Encyclopedia of Snow, Ice and Glaciers
 |publisher        = Springer Science & Business Media
 |url              = https://books.google.com/books?id=mKKtQR4T-1MC
 }}</ref>

==Precipitation==
[[File:Countries receiving snowfall.svg|right|thumb|Occurrence of snowfall:{{Legend|#54E4E4|All elevations}}
{{Legend |#57AFFD|All elevations, not in all areas}}
{{Legend|#0000FF|Higher elevations (mainly above 500 meters), below rarely}}
{{Legend|#EC74E4|Higher elevations (above 500 meters) only}}
{{Legend|#D300CA|Very high elevations (such as above 2,000 meters) only}}
{{Legend|#C0C0C0|None at any elevation}}]]
Snow develops in [[cloud]]s that themselves are part of a larger weather system. The physics of snow crystal development in clouds results from a complex set of variables that include [[moisture]] content and temperatures. The resulting shapes of the falling and fallen crystals can be classified into a number of basic shapes and combinations thereof. Occasionally, some plate-like, dendritic and stellar-shaped snowflakes can form under clear sky with a very cold temperature inversion present.<ref name = Classificationonground/>

===Cloud formation===
Snow clouds usually occur in the context of larger weather systems, the most important of which is the low-pressure area, which typically incorporates warm and cold fronts as part of its circulation. Two additional and locally productive sources of snow are lake-effect (also sea-effect) storms and elevation effects, especially in mountains.<ref>{{Cite book |last=Mölders |first=Nicole |url=https://www.google.com/books/edition/Lectures_in_Meteorology/nWr1AwAAQBAJ?hl=en&gbpv=1&dq=snow+cloud+formation+lake+and+mountain&pg=PA86&printsec=frontcover |title=Lectures in Meteorology |last2=Kramm |first2=Gerhard |date=2014-07-05 |publisher=Springer |isbn=978-3-319-02144-7 |pages=86 |language=en}}</ref>

====Low-pressure areas====
{{Main|Extratropical cyclone}}
[[File:Feb242007 blizzard.gif|thumb|right|Extratropical cyclonic snowstorm, February 24, 2007—(Click for animation.)]]

[[Extratropical cyclone|Mid-latitude cyclones]] are [[low-pressure area]]s which are capable of producing anything from cloudiness and mild [[Winter storm#Snow|snow storms]] to heavy [[blizzard]]s.<ref name="ExtraLessonMillUni">{{cite web| title = ESCI 241&nbsp;– Meteorology; Lesson 16&nbsp;– Extratropical Cyclones | author = DeCaria| publisher = Department of Earth Sciences, [[Millersville University]]| date = December 7, 2005| url = http://www.atmos.millersville.edu/~adecaria/ESCI241/esci241_lesson16_cyclones.html | access-date = June 21, 2009 |archive-url = https://web.archive.org/web/20080208224320/http://www.atmos.millersville.edu/~adecaria/ESCI241/esci241_lesson16_cyclones.html |archive-date = February 8, 2008}}</ref>  During a hemisphere's [[autumn|fall]], winter, and spring, the atmosphere over continents can be cold enough through the depth of the [[troposphere]] to cause snowfall. In the Northern Hemisphere, the northern side of the low-pressure area produces the most snow.<ref>
{{cite journal
 |last        = Tolme
 |first       = Paul
 |title       = Weather 101: How to track and bag the big storms
 |journal     = Ski Magazine
 |volume      = 69
 |issue       = 4
 |page       = 126
 |date        = December 2004
 |url         = https://books.google.com/books?id=t1DaXO7wF20C&pg=PA126
 |issn        = 0037-6159
 }}</ref> 

====Fronts====
{{Main|Weather front}}
[[File:Snowsquall line-Bourrasque neige frontal NOAA.png|thumb|right|Frontal snowsquall moving toward [[Boston]], [[Massachusetts]]]]
A [[cold front]], the leading edge of a cooler mass of air, can produce [[Snowsquall#Frontal snowsquall|frontal snowsqualls]]—an intense frontal [[convective]] line (similar to a [[rainband]]), when [[temperature]] is near freezing at the surface. The strong convection that develops has enough moisture to produce whiteout conditions at places which the line passes over as the wind causes intense blowing snow.<ref name=EC-2>{{Cite web
 |url         = http://www.ec.gc.ca/meteo-weather/default.asp?lang=En&n=46FBA88B-1#Snow
 |title       = Snow
 |work        = Winter Hazards
 |author      = Meteorological Service of Canada
 |author-link = Meteorological Service of Canada
 |publisher   = [[Environment Canada]]
 |date        = September 8, 2010
 |access-date  = October 4, 2010
 |url-status=live
 |archive-url  = https://web.archive.org/web/20110611163137/http://www.ec.gc.ca/meteo-weather/default.asp?lang=En&n=46FBA88B-1#Snow
 |archive-date = June 11, 2011
 |df          = mdy-all
}}</ref> This type of snowsquall generally lasts less than 30 minutes at any point along its path, but the motion of the line can cover large distances. Frontal squalls may form a short distance ahead of the surface cold front or behind the cold front where there may be a deepening low-pressure system or a series of [[Trough (meteorology)|trough]] lines which act similar to a traditional cold frontal passage.<ref>{{Cite book |last=Hill |first=Jerry D. |url=https://www.google.com/books/edition/Snow_Squalls_in_the_Lee_of_Lake_Erie_and/P2ovmzR_OiYC?hl=en&gbpv=1&dq=post-frontal+snow+squalls&pg=PA2&printsec=frontcover |title=Snow Squalls in the Lee of Lake Erie and Lake Ontario: A Review of the Literature |date=1971 |publisher=U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service Eastern Region |pages=3 |language=en}}</ref>

A [[warm front]] can produce snow for a period as warm, moist air overrides below-freezing air and creates precipitation at the boundary. Often, snow transitions to rain in the warm sector behind the front.<ref name=EC-2/>

====Lake and ocean effects====
{{Main|Lake-effect snow}}
[[File:Lake Effect Snow on Earth.jpg|thumb|Cold northwesterly wind over [[Lake Superior]] and [[Lake Michigan]] creating lake-effect snowfall]]

Lake-effect snow is produced during cooler atmospheric conditions when a cold air mass moves across long expanses of warmer [[lake]] water, warming the lower layer of air which picks up [[water vapor]] from the lake, rises up through the colder air above, freezes, and is deposited on the [[leeward]] (downwind) shores.<ref>{{cite web|url=http://www.noaa.gov/features/02_monitoring/lakesnow.html|title=NOAA - National Oceanic and Atmospheric Administration - Monitoring & Understanding Our Changing Planet|url-status=live|archive-url=https://web.archive.org/web/20150102173430/http://www.noaa.gov/features/02_monitoring/lakesnow.html|archive-date=January 2, 2015|df=mdy-all}}</ref><ref>{{cite web|url=http://www.comet.ucar.edu/class/smfaculty/byrd/sld012.htm |title=Fetch |url-status=dead |archive-url=https://web.archive.org/web/20080515101954/http://www.comet.ucar.edu/class/smfaculty/byrd/sld012.htm |archive-date=May 15, 2008 }}</ref>

The same effect occurring over bodies of salt water is termed ''ocean-effect'' or ''bay-effect snow''. The effect is enhanced when the moving air mass is uplifted by the [[orographic lift|orographic]] influence of higher elevations on the downwind shores. This uplifting can produce narrow but very intense bands of precipitation which may deposit at a rate of many inches of snow each hour, often resulting in a large amount of total snowfall.<ref name=mass>{{cite book |last= Mass |first= Cliff |title= The Weather of the Pacific Northwest |year= 2008 |publisher= [[University of Washington Press]] |isbn= 978-0-295-98847-4 |page= 60}}</ref>

The areas affected by lake-effect snow are called [[snowbelt]]s. These include areas east of the [[Great Lakes]], the west coasts of northern Japan, the [[Kamchatka Peninsula]] in Russia, and areas near the [[Great Salt Lake]], [[Black Sea]], [[Caspian Sea]], [[Baltic Sea]], and parts of the northern Atlantic Ocean.<ref name="SCHMID">Thomas W. Schmidlin. [https://kb.osu.edu/dspace/bitstream/1811/23329/1/V089N4_101.pdf Climatic Summary of Snowfall and Snow Depth in the Ohio Snowbelt at Chardon.] {{webarchive|url=https://web.archive.org/web/20080408225438/https://kb.osu.edu/dspace/bitstream/1811/23329/1/V089N4_101.pdf |date=April 8, 2008 }} Retrieved on March 1, 2008.</ref>

====Mountain effects====
{{Main|Precipitation types#Orographic}}
[[Orography|Orographic]] or [[relief]] snowfall is created when moist air is forced up the [[windward]] side of [[mountain]] ranges by a large-scale [[wind]] flow. The lifting of moist air up the side of a mountain range results in [[Adiabatic lapse rate|adiabatic]] cooling, and ultimately [[condensation]] and precipitation. Moisture is gradually removed from the air by this process, leaving [[Foehn wind|drier and warmer air]] on the descending, or [[leeward]], side.<ref name="MT">Physical Geography. [http://www.physicalgeography.net/fundamentals/8e.html CHAPTER 8: Introduction to the Hydrosphere (e). Cloud Formation Processes.] {{webarchive|url=https://web.archive.org/web/20081220230524/http://www.physicalgeography.net/fundamentals/8e.html |date=December 20, 2008 }} Retrieved on January 1, 2009.</ref> The resulting enhanced snowfall,<ref>{{Citation
 |first1        = Mark T.
 |last1         = Stoelinga
 |first2       = Ronald E.
 |last2        = Stewart
 |first3       = Gregory
 |last3        = Thompson
 |first4       = Julie M.
 |last4        = Theriault
 |editor-last  = Chow
 |editor-first = Fotini K.
 |display-editors=1
 |editor2=Stephan F.J. De Wekker
 |editor3=Bradley J. Snyder
 |title        = Mountain Weather Research and Forecasting: Recent Progress and Current Challenges
 |contribution = Micrographic processes within winter orographic cloud and precipitation systems
 |series       = Springer Atmospheric Sciences
 |year         = 2012
 |page         = 3
 |publisher    = Springer Science & Business Media
 |bibcode = 2013mwrf.book.....C
 |url          = https://books.google.com/books?id=ihjFd5Q8oPMC&pg=PA3
 |isbn         = 978-94-007-4098-3
 }}</ref> along with the [[Lapse rate|decrease in temperature]] with elevation,<ref>{{cite book|author=Mark Zachary Jacobson|title=Fundamentals of Atmospheric Modeling|publisher=Cambridge University Press|edition=2nd|year=2005|isbn=978-0-521-83970-9}}</ref> combine to increase snow depth and seasonal persistence of snowpack in snow-prone areas.<ref name = Snowenclyclopedia/><ref name=Singh>
{{cite book
 |last        = P.
 |first       = Singh
 |title       = Snow and Glacier Hydrology
 |publisher   = Springer Science & Business Media
 |series      = Water Science and Technology Library
 |volume      = 37
 |date        = 2001
 |page        = 75
 |url         = https://books.google.com/books?id=0VW6Tv0LVWkC&pg=PA75
 |isbn        = 978-0-7923-6767-3
 }}</ref>

[[Mountain waves]] have also been found to help enhance precipitation amounts downwind of mountain ranges by enhancing the lift needed for condensation and precipitation.<ref>{{cite journal|last1=Gaffin|first1=David M.|last2=Parker|first2=Stephen S.|last3=Kirkwood|first3=Paul D.|date=2003|title=An Unexpectedly Heavy and Complex Snowfall Event across the Southern Appalachian Region|journal=Weather and Forecasting|volume=18|issue=2|pages=224–235|bibcode=2003WtFor..18..224G|doi=10.1175/1520-0434(2003)018<0224:AUHACS>2.0.CO;2|doi-access=free}}</ref>

===Cloud physics===
{{Main|Snowflake}}
[[File:Snow day in Adachi Tokyo - 2018 1 22.webm|thumb|Snow falling in [[Tokyo]], [[Japan]]]]
[[File:Feathery Snow Crystals (2217830221).jpg|thumb|Freshly fallen snowflakes]]
A snowflake consists of roughly 10<sup>19</sup> water [[molecule]]s which are added to its core at different rates and in different patterns depending on the changing temperature and humidity within the atmosphere that the snowflake falls through on its way to the ground. As a result, snowflakes differ from each other though they follow similar patterns.<ref>{{cite web|url=http://news.nationalgeographic.com/news/2007/02/070213-snowflake.html|title="No Two Snowflakes the Same" Likely True, Research Reveals|author=John Roach|date=February 13, 2007|access-date=July 14, 2009|publisher=[[National Geographic Society|National Geographic]] News|url-status=dead|archive-url=https://web.archive.org/web/20100109031550/http://news.nationalgeographic.com/news/2007/02/070213-snowflake.html|archive-date=January 9, 2010|df=mdy-all}}</ref><ref>{{cite journal|title=Origin of diversity in falling snow|author=Jon Nelson|journal=Atmospheric Chemistry and Physics|date=September 26, 2008|doi=10.5194/acp-8-5669-2008|volume=8|issue=18|pages=5669–5682|df=mdy-all|bibcode=2008ACP.....8.5669N|doi-access=free}}</ref><ref>{{cite journal|url=http://www.aft.org/pubs-reports/american_educator/issues/winter04-05/Snowflake.pdf |title=Snowflake Science |author=Kenneth Libbrecht |journal=American Educator |date=Winter 2004–2005 |access-date=July 14, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20081128094655/http://www.aft.org/pubs-reports/american_educator/issues/winter04-05/Snowflake.pdf |archive-date=November 28, 2008 }}</ref>

Snow crystals form when tiny [[supercool]]ed cloud droplets (about 10&nbsp;[[micrometre|μm]] in diameter) [[freezing|freeze]]. These droplets are able to remain liquid at temperatures lower than {{convert|-18|°C|°F|0}}, because to freeze, a few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice. The droplet freezes around this "nucleus". In warmer clouds, an aerosol particle or "ice nucleus" must be present in (or in contact with) the droplet to act as a nucleus. Ice nuclei are very rare compared to cloud condensation nuclei on which liquid droplets form. Clays, desert dust, and biological particles can be nuclei.<ref name=Christner2008>{{cite journal
|author = Brent Q Christner
|author2=Cindy E Morris |author3=Christine M Foreman |author4=Rongman Cai |author5=David C Sands
 |year = 2008
|title = Ubiquity of Biological Ice Nucleators in Snowfall
|journal = Science
|volume = 319
|issue = 5867
|page = 1214
|doi = 10.1126/science.1149757
|pmid = 18309078
|bibcode=2008Sci...319.1214C|citeseerx=10.1.1.395.4918 |s2cid=39398426 }}</ref> Artificial nuclei include particles of [[silver iodide]] and [[dry ice]], and these are used to stimulate precipitation in [[cloud seeding]].<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=cloud+seeding&submit=Search|title=Cloud seeding|author=Glossary of Meteorology|year=2009|access-date=June 28, 2009|publisher=[[American Meteorological Society]]|url-status=dead|archive-url=https://web.archive.org/web/20120315161127/http://amsglossary.allenpress.com/glossary/search?p=1&query=cloud+seeding&submit=Search|archive-date=March 15, 2012|df=mdy-all}}</ref>

Once a droplet has frozen, it grows in the supersaturated environment—one where air is saturated with respect to ice when the temperature is below the freezing point. The droplet then grows by diffusion of water [[molecule]]s in the air (vapor) onto the ice crystal surface where they are collected. Because water droplets are so much more numerous than the ice crystals, the crystals are able to grow to hundreds of micrometers or millimeters in size at the expense of the water droplets by the [[Wegener–Bergeron–Findeisen process]]. These large crystals are an efficient source of precipitation, since they fall through the atmosphere due to their mass, and may collide and stick together in clusters, or aggregates. These aggregates are [[snowflake]]s, and are usually the type of ice particle that falls to the ground.<ref name="natgeojan07">{{cite journal|author=M. Klesius| title=The Mystery of Snowflakes| journal=National Geographic| volume=211| issue=1| year=2007| issn=0027-9358|page=20}}</ref> Although the ice is clear, scattering of light by the crystal facets and hollows/imperfections mean that the crystals often appear white in color due to [[diffuse reflection]] of the whole [[spectrum]] of [[light]] by the small ice particles.<ref>{{cite book|url=https://books.google.com/books?id=4T-aXFsMhAgC&pg=PA39|title=Hands-on Science: Light, Physical Science (matter) – Chapter 5: The Colors of Light|page=39|author=Jennifer E. Lawson|isbn=978-1-894110-63-1|year=2001|access-date=June 28, 2009|publisher=Portage & Main Press}}</ref>

===Classification of snowflakes===
{{Main||Snowflake#Classification}}
[[File:Snowflakeschapte00warriala-p11-p21-p29-p39.jpg|thumb|right|An early classification of snowflakes by [[Israel Perkins Warren]]<ref>
{{cite book
 |last        = Warren
 |first       = Israel Perkins
 |author-link = Israel Perkins Warren
 |title       = Snowflakes: a chapter from the book of nature
 |publisher   = American Tract Society
 |date        = 1863
 |location    = Boston
 |pages       = 164
 |url         = https://archive.org/details/snowflakeschapte00warriala
 |access-date = November 25, 2016
 |url-status=live
 |archive-url  = https://web.archive.org/web/20160909180658/https://archive.org/details/snowflakeschapte00warriala
 |archive-date = September 9, 2016
 |df          = mdy-all
}}</ref>]]

[[Micrography]] of thousands of snowflakes from 1885 onward, starting with [[Wilson Bentley|Wilson Alwyn Bentley]], revealed the wide diversity of snowflakes within a classifiable set of patterns.<ref>{{cite news|url=http://www.digitaljournal.com/article/263168|title=No two snowflakes are alike|date=December 7, 2008|author=Chris V. Thangham|access-date=July 14, 2009|work=Digital Journal|url-status=live|archive-url=https://web.archive.org/web/20091228011231/http://www.digitaljournal.com/article/263168|archive-date=December 28, 2009|df=mdy-all}}</ref> Closely matching snow crystals have been observed.<ref name="identical_crystals">{{cite news
 |author      = Randolph E. Schmid
 |title       = Identical snowflakes cause flurry
 |agency      = Associated Press
 |newspaper   = The Boston Globe
 |date        = June 15, 1988
 |access-date  = November 27, 2008
 |quote       = But there the two crystals were, side by side, on a glass slide exposed in a cloud on a research flight over Wausau, Wis.
 |url         = http://www.highbeam.com/doc/1P2-8066647.html
 |url-status=live
 |archive-url  = https://web.archive.org/web/20110624033612/http://www.highbeam.com/doc/1P2-8066647.html
 |archive-date = June 24, 2011
 |df          = mdy-all
}}</ref>

[[Ukichiro Nakaya]] developed a crystal morphology diagram, relating crystal shapes to the temperature and moisture conditions under which they formed, which is summarized in the following table.<ref name = Snowenclyclopedia/>
{| class="wikitable"
|+ Crystal structure morphology as a function of temperature and water saturation
|-
! colspan=2| Temperature range
! colspan=2| Saturation range
! colspan=2| Types of snow crystal
|-
!°C
!°F
!g/m<sup>3</sup>
!oz/cu yd
! ''below'' saturation
! ''above'' saturation
|-
| {{convert|0|to|-3.5|C|F|0|disp=table}}
| {{convert|0.0|to|0.5|g/m3|oz/cuyd|disp=table}}
| style="text-align:center;" | Solid plates
| style="text-align:center;" | Thin plates
Dendrites
|-
| {{convert|-3.5|to|-10|C|F|0|disp=table}}
| {{convert|0.5|to|1.2|g/m3|oz/cuyd|disp=table}}
| style="text-align:center;" | Solid prisms
Hollow prisms
| style="text-align:center;" | Hollow prisms
Needles
|-
| {{convert|-10|to|-22|C|F|0|disp=table}}
| {{convert|1.2|to|1.4|g/m3|oz/cuyd|disp=table}}
| style="text-align:center;" | Thin plates
Solid plates
| style="text-align:center;" | Sectored plates
Dendrites
|-
| {{convert|-22|to|-40|C|F|0|disp=table}}
| {{convert|1.2|to|0.1|g/m3|oz/cuyd|disp=table}}
| style="text-align:center;" | Thin plates
Solid plates
| style="text-align:center;" | Columns
Prisms
|}
Nakaya discovered that the shape is also a function of whether the prevalent moisture is above or below saturation. Forms below the saturation line tend more toward solid and compact while crystals formed in supersaturated air tend more toward lacy, delicate, and ornate. Many more complex growth patterns also form, which include side-planes, bullet-rosettes, and planar types, depending on the conditions and ice nuclei.<ref name=BaileyHallett>{{cite journal
|author = Matthew Bailey
|author2=John Hallett
 |year = 2004
|title = Growth rates and habits of ice crystals between −20 and −70C
|journal = Journal of the Atmospheric Sciences
|volume = 61
|issue = 5
|pages = 514–544
|doi = 10.1175/1520-0469(2004)061<0514:GRAHOI>2.0.CO;2
|bibcode = 2004JAtS...61..514B|doi-access = free
}}</ref><ref>{{cite web|author=Kenneth G. Libbrecht|url=http://www.its.caltech.edu/~atomic/snowcrystals/primer/primer.htm|title=A Snowflake Primer|date=October 23, 2006|publisher=[[California Institute of Technology]]|access-date=June 28, 2009|url-status=live|archive-url=https://web.archive.org/web/20090710022028/http://www.its.caltech.edu/~atomic/snowcrystals/primer/primer.htm|archive-date=July 10, 2009|df=mdy-all}}</ref><ref>{{cite journal|author=Kenneth G. Libbrecht|title=The Formation of Snow Crystals|journal=American Scientist|volume=95|issue=1|pages=52–59|date=January–February 2007|doi=10.1511/2007.63.52}}</ref> If a crystal has started forming in a column growth regime at around {{convert|-5|C|F|0}} and then falls into the warmer plate-like regime, plate or dendritic crystals sprout at the end of the column, producing so called "capped columns".<ref name="natgeojan07" />

Magono and Lee devised a classification of freshly formed snow crystals that includes 80 distinct shapes. They documented each with micrographs.<ref name = magono-lee>
{{Citation
 | last1 = Magono
 | first1 = Choji
 | last2 = Lee
 | first2 = Chung Woo
 | title = Meteorological Classification of Natural Snow Crystals
 | place = Hokkaido
 | journal = Journal of the Faculty of Science
 | volume = 3
 | issue = 4
 | date = 1966
 | edition = Geophysics
 | series = 7
 | pages = 321–335
 | language = en
 | hdl = 2115/8672
 }}</ref>

==Accumulation==
[[File:Earth-satellite-seasons.gif|thumb|upright=1.2|An animation of seasonal snow changes, based on satellite imagery]]
Snow accumulates from a series of snow events, punctuated by freezing and thawing, over areas that are cold enough to retain snow seasonally or perennially. Major snow-prone areas include the [[Arctic]] and [[Antarctic]], the Northern Hemisphere, and alpine regions. The liquid equivalent of snowfall may be evaluated using a [[snow gauge]]<ref>{{cite web|url=http://www.on.ec.gc.ca/skywatchers/ontario/wx_office_tour/compound/snow_e.html |title=Nipher Snow Gauge |publisher=On.ec.gc.ca |date=August 27, 2007 |access-date=August 16, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110928121043/http://www.on.ec.gc.ca/skywatchers/ontario/wx_office_tour/compound/snow_e.html |archive-date=September 28, 2011 }}</ref> or with a standard [[rain gauge]], adjusted for winter by removal of a funnel and inner cylinder.<ref>{{cite news|author=National Weather Service Office, Northern Indiana|author-link=National Weather Service|publisher=[[National Weather Service]] Central Region Headquarters|url=http://www.crh.noaa.gov/iwx/program_areas/coop/8inch.php|title=8 Inch Non-Recording Standard Rain Gage|access-date=January 2, 2009|date=April 13, 2009|url-status=live|archive-url=https://web.archive.org/web/20081225234123/http://www.crh.noaa.gov/iwx/program_areas/coop/8inch.php|archive-date=December 25, 2008|df=mdy-all}}</ref> Both types of gauges melt the accumulated snow and report the amount of water collected.<ref>[[National Weather Service]] Office [[Binghamton, New York]] (2009). [http://www.erh.noaa.gov/bgm/spotters_skywarn/precip4.shtml Raingauge Information.] {{webarchive|url=https://web.archive.org/web/20081013090524/http://www.erh.noaa.gov/bgm/spotters_skywarn/precip4.shtml |date=October 13, 2008 }} Retrieved on January 2, 2009.</ref> At some [[automatic weather station]]s an ultrasonic snow depth sensor may be used to augment the precipitation gauge.<ref>{{cite web|url=http://www.on.ec.gc.ca/skywatchers/ontario/wx_office_tour/compound/geonor_e.html |title=All-Weather Precipitation Gauge |publisher=On.ec.gc.ca |date=August 27, 2007 |access-date=August 16, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110928121114/http://www.on.ec.gc.ca/skywatchers/ontario/wx_office_tour/compound/geonor_e.html |archive-date=September 28, 2011 }}</ref>

===Event===
[[File:Winter Storm Jonas 2016 NYC Pershing Square.jpg|thumb|[[New York City]] during a [[January 2016 United States blizzard|2016 blizzard]], which produced strong winds and record-breaking snowfall.]]

[[Snow flurry]], [[Shower (precipitation)|snow shower]], [[snow storm]] and [[blizzard]] describe snow events of progressively greater duration and intensity.<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=snow-flurry1|author=Glossary of Meteorology|year=2009|access-date=June 28, 2009|publisher=[[American Meteorological Society]]|title=Snow flurry|url-status=dead|archive-url=https://web.archive.org/web/20071127144615/http://amsglossary.allenpress.com/glossary/search?id=snow-flurry1|archive-date=November 27, 2007|df=mdy-all}}</ref> A [[blizzard]] is a weather condition involving snow and has varying definitions in different parts of the world. In the [[United States]], a blizzard occurs when two conditions are met for a period of three hours or more: a sustained wind or frequent gusts to {{convert|sp=us|35|mph|m/s}}, and sufficient snow in the air to reduce visibility to less than {{convert|sp=us|0.4|km|mi}}.<ref>{{cite web |title = National Weather Service Glossary |url = http://www.nws.noaa.gov/glossary/index.php?letter=b |publisher = [[National Weather Service]] |year = 2009 |access-date = July 12, 2009 |url-status=live |archive-url = https://web.archive.org/web/20090509183315/http://www.nws.noaa.gov/glossary/index.php?letter=b |archive-date = May 9, 2009 |df = mdy-all }}</ref> In [[Canada]] and the [[United Kingdom]], the criteria are similar.<ref>{{cite web|title=Blizzards |url=http://www.mb.ec.gc.ca/air/wintersevere/blizzards.en.html |work=Winter Severe Weather |publisher=Environment Canada |date=September 4, 2002 |access-date=July 12, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090211120800/http://www.mb.ec.gc.ca/air/wintersevere/blizzards.en.html |archive-date=February 11, 2009 }}</ref><ref>{{cite web|title= Key to flash warning criteria |url= http://www.metoffice.gov.uk/weather/uk/guide/key_warnings.html |archive-url= https://web.archive.org/web/20101229172227/http://www.metoffice.gov.uk/weather/uk/guide/key_warnings.html |archive-date= December 29, 2010 |author= Met Office|author-link= Met Office |date=November 19, 2008|access-date= July 12, 2009}}</ref> While heavy snowfall often occurs during blizzard conditions, falling snow is not a requirement, as [[blowing snow]] can create a [[ground blizzard]].<ref>{{cite web |title = Blizzards |url = http://www.wrh.noaa.gov/fgz/science/blizzard.php?wfo=fgz |author = [[National Weather Service]] Forecast Office, [[Flagstaff, Arizona]] |publisher = [[National Weather Service]] Western Region Headquarters |access-date = July 12, 2009 |date = May 24, 2007 |url-status=live |archive-url = https://web.archive.org/web/20090115090647/http://www.wrh.noaa.gov/fgz/science/blizzard.php?wfo=fgz |archive-date = January 15, 2009 |df = mdy-all }}</ref>

Snowstorm intensity may be categorized by visibility and depth of accumulation.<ref>{{cite web|url=http://www.nws.noaa.gov/om/brochures/wntrstm.htm |title=Winter Storms...the Deceptive Killers |publisher=United States [[Department of Commerce]] |date=November 1991 |access-date=June 28, 2009 |author=National Oceanic and Atmospheric Administration |author-link=National Oceanic and Atmospheric Administration |url-status=dead |archive-url=https://web.archive.org/web/20090608185155/http://www.nws.noaa.gov/om/brochures/wntrstm.htm |archive-date=June 8, 2009 }}</ref> Snowfall's intensity is determined by [[visibility]], as follows:<ref>{{cite web|title=Snow|author=Glossary of Meteorology|url=http://amsglossary.allenpress.com/glossary/search?id=snow1|publisher=[[American Meteorological Society]]|year=2009|access-date=June 28, 2009|url-status=dead|archive-url=https://web.archive.org/web/20090220090504/http://amsglossary.allenpress.com/glossary/search?id=snow1|archive-date=February 20, 2009|df=mdy-all}}</ref>
* ''Light'': visibility greater than {{convert|sp=us|1|km|mi|sigfig=1}}
* ''Moderate'': visibility restrictions between {{convert|sp=us|0.5|and|1|km|mi|sigfig=1}}
* ''Heavy'': visibility is less than {{convert|sp=us|0.5|km|mi|sigfig=1}}
[[Snowsquall]]s may deposit snow in bands that extend from bodies of water as lake-event weather or result from the passage of an upper-level front.<ref name="popsci/nasa-snowstorm">{{cite news |date=3 February 2022 |title=NASA's storm-chasing planes fly through blizzards to improve snowfall forecasts |work=[[Popular Science]] |url=https://www.popsci.com/science/nasa-planes-improve-snowstorm-forecasts/ |access-date=9 March 2023}}</ref><ref name="weather/bandedsnowfall">{{cite web |author1=NOAA |title=What causes bands of heavy snowfall? |url=https://www.weather.gov/fsd/news_bandedsnowfall_20151121 |access-date=9 March 2023 |website=weather.gov |publisher=US Department of Commerce |language=EN-US}}</ref><ref name="nbcmontana/snow-bands">{{cite web |last1=Coombs |first1=Mitchel |date=28 November 2022 |title=3D Weather: Science of snow bands |url=https://nbcmontana.com/news/local/3d-weather-science-of-snow-bands |access-date=9 March 2023 |website=[[KECI]] |language=en}}</ref>

The ''International Classification for Seasonal Snow on the Ground'' defines "height of new snow" as the depth of freshly fallen snow, in centimeters as measured with a ruler, that accumulated on a [[snowboard (meteorology)|snowboard]] during an observation period of 24 hours, or other observation interval. After the measurement, the snow is cleared from the board and the board is placed flush with the snow surface to provide an accurate measurement at the end of the next interval.<ref name = Classificationonground/> Melting, compacting, blowing and drifting contribute to the difficulty of measuring snowfall.<ref>{{cite web|url=http://www.crh.noaa.gov/iwx/program_areas/snow_spotters/SnowMeasurement.pdf|title=Snow Measurement Guidelines for National Weather Service Snow Spotters|author=National Weather Service Forecast Office Northern Indiana|author-link=National Weather Service|publisher=National Weather ServiceCentral Region Headquarters|date=October 2004|url-status=live|archive-url=https://web.archive.org/web/20100215064901/http://www.crh.noaa.gov/iwx/program_areas/snow_spotters/SnowMeasurement.pdf|archive-date=February 15, 2010|df=mdy-all}}</ref>

===Distribution===
[[File:Snow-covered fir trees.jpg|thumb|Snow-covered trees in [[Kuusamo]], [[Finland]]]]
Glaciers with their permanent snowpacks cover about 10% of the earth's surface, while seasonal snow covers about nine percent,<ref name = Snowenclyclopedia/> mostly in the Northern Hemisphere, where seasonal snow covers about {{convert|40|e6km2}}, according to a 1987 estimate.<ref>
{{cite journal
 |last1        = Chang
 |first1       = A.T.C.
 |last2       = Foster
 |first2      = J.L.
 |last3       = Hall
 |first3      = D.K.
 |title       = NIMBUS-7 SMMR derived global snow parameters
 |journal     = Annals of Glaciology
 |volume      = 9
 |date        = 1987
 |df          = mdy-all
|doi = 10.1017/S0260305500200736
 |pages = 39–44
 |doi-access= free
 }}</ref> A 2007 estimate of snow cover over the Northern Hemisphere suggested that, on average, snow cover ranges from a minimum extent of {{convert|2|e6km2}} each August to a maximum extent of {{convert|45|e6km2}} each January or nearly half of the land surface in that hemisphere.<ref>
{{Citation
 | last = Lemke
 | first = P.
 | display-authors = etal
 | editor-last = Solomon
 | editor-first = S.
 | display-editors = etal
 | contribution = Observations: Changes in snow, ice and frozen ground
 | title = Climate Change 2007: The Physical Science Basis
 | year = 2007
 | pages = 337–383
 | place = New York
 | publisher = Cambridge Univ. Press
 }}</ref><ref name=Déry>
{{Citation
 |last1        = Déry
 |first1       = S. J
 |last2       = Brown
 |first2      = R. D.
 |title       = Recent Northern Hemisphere snow cover extent trends and implications for the snow-albedo feedback
 |journal     = Geophysical Research Letters
 |volume      = 34
 |issue       = L22504
 |pages       = L22504
 |year        = 2007
 |doi         = 10.1029/2007GL031474
 |bibcode       = 2007GeoRL..3422504D
 |doi-access= free
 }}</ref> A study of Northern Hemisphere snow cover extent for the period 1972–2006 suggests a reduction of {{convert|0.5|e6km2}} over the 35-year period.<ref name = Déry/>

===Records===
The following are world records regarding snowfall and snowflakes:
* ''Highest seasonal total snowfall'' – The world record for the highest seasonal total snowfall was measured in the United States at [[Mt. Baker Ski Area]], outside of the city of [[Bellingham, Washington]] during the 1998–1999 season. Mount Baker received {{convert|2896|cm|ft|abbr=on}} of snow,<ref>{{cite web|url=https://www.usatoday.com/weather/news/1999/wsnorcrd.htm|title=NOAA: Mt. Baker snowfall record sticks|work=[[USA Today]]|date=August 3, 1999|access-date=June 30, 2009|url-status=live|archive-url=https://web.archive.org/web/20090424104329/http://www.usatoday.com/weather/news/1999/wsnorcrd.htm|archive-date=April 24, 2009|df=mdy-all}}</ref> thus surpassing the previous record holder, [[Mount Rainier]], Washington, which during the 1971–1972 season received {{convert|2850|cm|ft|abbr=on}} of snow.<ref>{{cite web|url=http://www.nps.gov/archive/mora/interp/faq.htm|archive-url=https://web.archive.org/web/20070221204740/http://www.nps.gov/archive/mora/interp/faq.htm|url-status=dead|archive-date=February 21, 2007|title=Frequently Asked Questions|author=Mount Rainier National Park|author-link=Mount Rainier National Park|publisher=[[National Park Service]]|date=April 14, 2006|access-date=June 30, 2009}}</ref>
* ''Highest seasonal average annual snowfall'' – The world record for the highest average annual snowfall is {{convert|1764|cm|ft|abbr=on}},<ref>{{cite web | url = http://www.data.jma.go.jp/obd/stats/etrn/view/nml_amd_ym.php?prec_no=31&block_no=1079&year=&month=&day=&view= | title = JMA | access-date = November 12, 2012 | publisher = JMA | language = ja | url-status=live | archive-url = https://web.archive.org/web/20130618204127/http://www.data.jma.go.jp/obd/stats/etrn/view/nml_amd_ym.php?prec_no=31&block_no=1079&year=&month=&day=&view= | archive-date = June 18, 2013 | df = mdy-all }}</ref> measured in [[Sukayu Onsen]], Japan for the period of 1981–2010.{{cn|date=May 2025}}
* ''Largest snowflake'' – According to ''[[Guinness World Records]],'' the world's largest snowflake fell in January 1887 outside present-day [[Miles City, Montana|Miles City]], [[Montana]]. It measured {{convert|38|cm|in|abbr=on}} in diameter.<ref>{{cite news |url=https://www.nytimes.com/2007/03/20/science/20snow.html |title=Giant Snowflakes as Big as Frisbees? Could Be |newspaper=New York Times |author=William J. Broad |date=March 20, 2007 |access-date=July 12, 2009 |url-status=live |archive-url=https://web.archive.org/web/20111104033402/http://www.nytimes.com/2007/03/20/science/20snow.html |archive-date=November 4, 2011 |df=mdy-all }}</ref>

The cities (more than 100,000 inhabitants) with the highest annual snowfall are [[Aomori]] (792&nbsp;cm), [[Sapporo]] (485&nbsp;cm) and [[Toyama, Toyama|Toyama]] (363&nbsp;cm) in [[Japan]], followed by [[St. John's, Newfoundland and Labrador|St. John's]] (332&nbsp;cm) and [[Quebec City]] (315&nbsp;cm) in [[Canada]], and [[Syracuse, NY]] (325&nbsp;cm).<ref>{{cite web |title=Top 10 snowiest major cities around the world |url=https://www.accuweather.com/en/weather-news/top-10-snowiest-major-cities-around-the-world/375130 |website=Accuweather |access-date=4 March 2023}}</ref>

==Metamorphism==
[[File:Sparkling-snow.crystals.jpg|thumb|Fresh snow beginning to metamorphose: The surface shows wind packing and [[sastrugi]]. In the foreground are [[hoar frost]] crystals, formed by refrozen water vapor emerging to the cold surface.]]
[[File:Svalbard-Sastrugi-Snow.jpg|thumb|Sastrugi formed during a blizzard just a few hours earlier.]]
According to the International Association of Cryospheric Sciences, ''snow metamorphism'' is "the transformation that the snow undergoes in the period from deposition to either melting or passage to glacial ice".<ref name="Classificationonground" /> Starting as a powdery deposition, snow becomes more granular when it begins to compact under its own weight, be blown by the wind, sinter particles together and commence the cycle of melting and refreezing. Water vapor plays a role as it deposits ice crystals, known as [[hoar frost]], during cold, still conditions.<ref>{{cite book|url=https://books.google.com/books?id=0Bpscs7Gqb8C&pg=PA71|title=The Avalanche Handbook|author1=David McClung  |author2=Peter Schaerer |name-list-style=amp |pages=49–51|isbn=978-0-89886-809-8|publisher=The Mountaineers Books|year=2006|access-date=July 7, 2009}}</ref> During this transition, snow "is a highly porous, sintered material made up of a continuous ice structure and a continuously connected pore space, forming together the snow microstructure". Almost always near its melting temperature, a snowpack is continually transforming these properties wherein all three phases of water may coexist, including liquid water partially filling the pore space. After deposition, snow progresses on one of two paths that determine its fate, either by ''ablation'' (mostly by melting) from a snowfall or seasonal snowpack, or by transitioning from [[firn]] (multi-year snow) into ''glacier ice''.<ref name = Classificationonground/>

===Seasonal===
{{Main|Snowpack|Névé}}
Over the course of time, a snowpack may settle under its own weight until its density is approximately 30% of water. Increases in density above this initial compression occur primarily by melting and refreezing, caused by temperatures above freezing or by direct solar radiation. In colder climates, snow lies on the ground all winter. By late spring, snow densities typically reach a maximum of 50% of water.<ref>{{cite web|url=http://cdec.water.ca.gov/snow/misc/density.html|author=California Data Exchange Center|publisher=Department of Water Resources California|title=Depth and Density|year=2007|access-date=July 8, 2009|url-status=live|archive-url=https://web.archive.org/web/20090713000814/http://cdec.water.ca.gov/snow/misc/density.html|archive-date=July 13, 2009|df=mdy-all}}</ref> Snow that persists into summer evolves into [[névé]], granular snow, which has been partially melted, refrozen and compacted. Névé has a minimum [[density]] of {{convert|500|kg/m3|lb/ft3}}, which is [[Density#Water|roughly half]] of the density of liquid water.<ref>{{cite web|author=Glossary of Meteorology|title=Firn|url=http://amsglossary.allenpress.com/glossary/search?id=firn1|year=2009|access-date=June 30, 2009|publisher=[[American Meteorological Society]]|url-status=dead|archive-url=https://web.archive.org/web/20070824054449/http://amsglossary.allenpress.com/glossary/search?id=firn1|archive-date=August 24, 2007|df=mdy-all}}</ref>

===Firn===
{{Main|Firn}}
[[File:Firn field on the top of Säuleck.jpg|thumb|right|[[Firn]]—metamorphosed multi-year snow]]
Firn is snow that has persisted for multiple years and has been [[Recrystallization (chemistry)|recrystallized]] into a substance denser than [[névé]], yet less dense and hard than glacial [[ice]]. Firn resembles caked sugar and is very resistant to shovelling. Its density generally ranges from {{convert|550|to|830|kg/m3|lb/ft3}}, and it can often be found underneath the snow that accumulates at the head of a [[glacier]]. The minimum altitude that firn accumulates on a glacier is called the ''firn limit'', ''firn line'' or ''snowline''.<ref name = Snowenclyclopedia/><ref name="Glacialprocess">
{{cite web|url=http://www.physicalgeography.net/fundamentals/10ae.html|title=CHAPTER 10: Introduction to the Lithosphere—Glacial Processes|last1=Pidwirny|first1=Michael|last2=Jones|first2=Scott|date=2014|website=PhysicalGeography.net|publisher=University of British Columbia, Okanagan|access-date=2018-12-20}}</ref>

==Movement==
There are four main mechanisms for movement of deposited snow: ''drifting'' of unsintered snow, ''avalanches'' of accumulated snow on steep slopes, ''snowmelt'' during thaw conditions, and the ''movement of glaciers'' after snow has persisted for multiple years and metamorphosed into glacier ice.<ref>{{Cite book |last=Singh |first=Vijay P. |url=https://www.google.com/books/edition/Encyclopedia_of_Snow_Ice_and_Glaciers/tl2oKpXE0cMC?hl=en&gbpv=1&dq=mechanisms+of+snow+movement&pg=PA538&printsec=frontcover |title=Encyclopedia of Snow, Ice and Glaciers |last2=Singh |first2=Pratap |last3=Haritashya |first3=Umesh K. |date=2011-06-29 |publisher=Springer Science & Business Media |isbn=978-90-481-2642-2 |pages=538 |language=en}}</ref>

===Drifting===
[[File:Long Mynd snowdrift.jpeg|thumb|right|Snow drifts forming around downwind obstructions]]
When powdery snow drifts with the [[wind]] from the location where it originally fell,<ref>{{cite web|url=http://www.cocorahs.org/media/docs/KS/CoCoRaHS%20Snow.PDF|title=CoCoRaHS in the Cold – Measuring in Snowy Weather|publisher=Colorado Climate Center|author=Joy Haden|date=February 8, 2005|access-date=July 12, 2009|url-status=live|archive-url=https://web.archive.org/web/20110718172302/http://www.cocorahs.org/media/docs/KS/CoCoRaHS%20Snow.PDF|archive-date=July 18, 2011|df=mdy-all}}</ref> forming deposits with a depth of several meters in isolated locations.<ref>{{cite news|url=https://www.telegraph.co.uk/topics/weather/4434935/Snow-Britain-Snow-drifts-and-blizzards-of-the-past.html|title=Snow Britain: Snow drifts and blizzards of the past|author=Caroline Gammel|date=February 2, 2009|access-date=July 12, 2009|publisher=Telegraph Media Group|url-status=dead|archive-url=https://web.archive.org/web/20090205075802/http://www.telegraph.co.uk/topics/weather/4434935/Snow-Britain-Snow-drifts-and-blizzards-of-the-past.html|archive-date=February 5, 2009|df=mdy-all}}</ref> After attaching to hillsides, blown snow can evolve into a snow slab, which is an avalanche hazard on steep slopes.<ref name="McClung 2006"/>

===Avalanche===
{{Main|Avalanche}}
[[File:2007-02-15-CLB-Couloir2-1c.JPG|thumb|A powder snow avalanche]]
An avalanche (also called a snowslide or snowslip) is a rapid flow of snow down a sloping surface. Avalanches are typically triggered in a starting zone from a mechanical failure in the snowpack (slab avalanche) when the forces on the snow exceed its strength but sometimes only with gradually widening (loose snow avalanche). After initiation, avalanches usually accelerate rapidly and grow in mass and volume as they [[Entrainment (physical geography)|entrain]] more snow. If the avalanche moves fast enough some of the snow may mix with the air forming a powder snow avalanche, which is a type of [[gravity current]]. They occur in three major mechanisms:<ref name="McClung 2006">McClung, David and Shaerer, Peter: The Avalanche Handbook, The Mountaineers: 2006. {{ISBN|978-0-89886-809-8}}</ref>
* ''Slab avalanches'' occur in snow that has been deposited, or redeposited by wind. They have the characteristic appearance of a block (slab) of snow cut out from its surroundings by fractures. These account for most back-country fatalities.
* ''[[Powder snow avalanche]]s'' result from a deposition of fresh dry powder and generate a powder cloud, which overlies a dense avalanche. They can exceed speeds of {{convert|300|kph||abbr=|sp=us}}, and masses of {{convert|10000000|tonnes}}; their flows can travel long distances along flat valley bottoms and even uphill for short distances.
* ''Wet snow avalanches'' are a low-velocity suspension of snow and water, with the flow confined to the surface of the pathway.<ref name="McClung 2006"/> The low speed of travel is due to the friction between the sliding surface of the pathway and the water saturated flow. Despite the low speed of travel (~{{convert|10|to|40|km/h|0|abbr=|sp=us}}), wet snow avalanches are capable of generating powerful destructive forces, due to the large mass, and density.<ref>{{Cite book |last=Earthsong |first=Glen |url=https://www.google.com/books/edition/AVALANCHE_SPEED_FACTORS/F4NQEQAAQBAJ?hl=en&gbpv=1&dq=Wet+avalanche+speed+and+destruction&pg=PT32&printsec=frontcover |title=Avalanche Speed Factors |date=2025 |publisher=Publifye AS |isbn=978-82-352-2867-3 |language=en}}</ref><ref name=":0">{{Cite book |last=Army |first=United States Department of the |url=https://www.google.com/books/edition/Field_Manual/AsUABYvaIFoC?hl=en&gbpv=1&dq=Wet+avalanche+speed+and+destruction&pg=PA1-IA33&printsec=frontcover |title=Field Manual |date=1980 |publisher=U.S. Government Printing Office |pages=F-6 |language=en}}</ref>

===Melting===
[[File:1997 Red River Flood Grand Forks.jpg|thumb|right|Snowmelt-induced flooding of the [[Red River of the North]] in [[1997 Red River flood|1997]]]]
Many rivers originating in mountainous or high-latitude regions receive a significant portion of their flow from snowmelt. This often makes the river's flow highly seasonal resulting in periodic [[flooding]]<ref name="Howard Perlman">{{cite web|url=http://ga.water.usgs.gov/edu/watercyclesnowmelt.html|title=The Water Cycle: Snowmelt Runoff|author=Howard Perlman|publisher=[[United States Geological Survey]]|date=May 13, 2009|access-date=July 7, 2009|url-status=dead|archive-url=https://web.archive.org/web/20090813020946/http://ga.water.usgs.gov/edu/watercyclesnowmelt.html|archive-date=August 13, 2009|df=mdy-all}}</ref> during the spring months and at least in dry mountainous regions like the mountain West of the US or most of [[Iran]] and [[Afghanistan]], very low flow for the rest of the year. In contrast, if much of the melt is from [[glaciated]] or nearly glaciated areas, the melt continues through the warm season, with peak flows occurring in mid to late summer.<ref>{{cite web|url=http://watershed.ucdavis.edu/copper_river/background/data/BowersoxCopper.pdf|title=Hydrology of a Glacial Dominated System, Copper River, Alaska|author=Randy Bowersox|page=2|access-date=July 8, 2009|date=June 20, 2002|publisher=[[University of California]]-Davis|url-status=live|archive-url=https://web.archive.org/web/20100612005951/http://watershed.ucdavis.edu/copper_river/background/data/BowersoxCopper.pdf|archive-date=June 12, 2010|df=mdy-all}}</ref>

===Glaciers===
{{Main|Glacier}}
[[File:Glaciar Perito Moreno22 - Argentina.JPG|thumb|The terminus of the [[Perito Moreno Glacier]] in the [[Argentino Lake]].]]

Glaciers form where the accumulation of snow and ice exceeds ablation. The area in which an alpine glacier forms is called a cirque (corrie or cwm), a typically armchair-shaped geological feature, which collects snow and where the snowpack compacts under the weight of successive layers of accumulating snow, forming névé. Further crushing of the individual snow crystals and reduction of entrapped air in the snow turns it into glacial ice. This glacial ice will fill the cirque until it overflows through a geological weakness or an escape route, such as the gap between two mountains. When the mass of snow and ice is sufficiently thick, it begins to move due to a combination of surface slope, gravity and pressure. On steeper slopes, this can occur with as little as {{convert|15|m|ft|abbr=on}} of snow-ice.<ref name = Snowenclyclopedia/>

==Science==
{{Main|Snow science}}
Scientists study snow at a wide variety of scales that include the [[physics]] of [[chemical bonds]] and [[Cloud physics|clouds]]; the distribution, accumulation, metamorphosis, and ablation of snowpacks; and the contribution of snowmelt to river [[hydraulics]] and ground [[hydrology]]. In doing so, they employ a variety of instruments to observe and measure the phenomena studied. Their findings contribute to knowledge applied by [[engineer]]s, who adapt vehicles and structures to snow, by [[agronomist]]s, who address the availability of snowmelt to [[agriculture]], and those, who design equipment for sporting activities on snow. Scientists develop and others employ snow classification systems that describe its physical properties at scales ranging from the individual crystal to the aggregated snowpack. A sub-specialty is [[avalanche]]s, which are of concern to engineers and outdoor sports people, alike.<ref name=":0" />

Snow science addresses how snow forms, its distribution, and processes affecting how snowpacks change over time. Scientists improve storm forecasting, study global snow cover and its effect on climate, glaciers, and water supplies around the world. The study includes physical properties of the material as it changes, bulk properties of in-place snow packs, and the aggregate properties of regions with snow cover. In doing so, they employ on-the-ground physical measurement techniques to establish [[ground truth]] and [[remote sensing]] techniques to develop understanding of snow-related processes over large areas.<ref>
{{cite web
 |url         = https://nsidc.org/cryosphere/snow/science
 |title       = All About Snow—Snow Science
 |date        = 2016
 |website     = National Snow and Ice Data Center
 |publisher   = University of Colorado, Boulder
 |access-date = November 30, 2016
 |url-status=live
 |archive-url  = https://web.archive.org/web/20161201020029/https://nsidc.org/cryosphere/snow/science
 |archive-date = December 1, 2016
 |df          = mdy-all
}}</ref>

===Measurement and classification===
{{See also|Classifications of snow}}
In the field, snow scientists often excavate a snow pit within which to make basic measurements and observations. Observations can describe features caused by wind, water percolation, or snow unloading from trees. Water percolation into a snowpack can create flow fingers and ponding or flow along capillary barriers, which can refreeze into horizontal and vertical solid ice formations within the snowpack. Among the measurements of the properties of snowpacks that the ''International Classification for Seasonal Snow on the Ground'' includes are: snow height, snow water equivalent, snow strength, and extent of snow cover. Each has a designation with a code and detailed description. The classification extends the prior classifications of Nakaya and his successors to related types of precipitation and are quoted in the following table:<ref name = Classificationonground/>
[[File:Taku glacier firn ice sampling.png|thumb|right|Snow pit on the surface of a glacier, profiling snow properties where the snow becomes increasingly dense with depth as it turns to ice]]
{| class="wikitable"
|+ Frozen precipitation particles, related to snow crystals
|-
! Subclass
! Shape
! Physical process
|-
| [[Graupel]]
| Heavily rimed particles, spherical, conical, hexagonal or irregular in shape
| Heavy riming of particles by accretion of supercooled water droplets
|-
| [[Hail]]
| Laminar internal structure, translucent or milky glazed surface
| Growth by accretion of supercooled water, size: >5&nbsp;mm
|-
| [[Ice pellets]]
| Transparent, mostly small spheroids
| Freezing of raindrops or refreezing of largely melted snow crystals or snowflakes (sleet). Graupel or snow pellets encased in thin ice layer (small hail). Size: both 5&nbsp;mm
|-
| [[Hard rime|Rime]]
| Irregular deposits or longer cones and needles pointing into the wind
| Accretion of small, supercooled fog droplets frozen in place. Thin breakable crust forms on snow surface if process continues long enough.
|}
''All are formed in cloud, except for rime, which forms on objects exposed to supercooled moisture.''

It also has a more extensive classification of deposited snow than those that pertain to airborne snow. The categories include both natural and man-made snow types, descriptions of snow crystals as they metamorphose and melt, the development of hoar frost in the snow pack and the formation of ice therein. Each such layer of a snowpack differs from the adjacent layers by one or more characteristics that describe its microstructure or density, which together define the snow type, and other physical properties. Thus, at any one time, the type and state of the snow forming a layer have to be defined because its physical and mechanical properties depend on them. Physical properties include microstructure, grain size and shape, snow density, liquid water content, and temperature.<ref name=Classificationonground>
{{Citation
 |last1        = Fierz
 |first1       = C.
 |last2       = Armstrong
 |first2      = R.L.
 |last3       = Durand
 |first3      = Y.
 |last4       = Etchevers
 |first4      = P.
 |last5       = Greene
 |first5      = E.
 |display-authors=5
 |author6=McClung, D.M.
 |author7=Nishimura, K.
 |author8=Satyawali, P.K.
 |author9=Sokratov, S.A.
 |title       = The International Classification for Seasonal Snow on the Ground
 |place       = Paris
 |publisher   = UNESCO
 |series      = IHP-VII Technical Documents in Hydrology
 |volume      = 83
 |year        = 2009
 |pages       = 80
 |url         = http://unesdoc.unesco.org/images/0018/001864/186462e.pdf
 |access-date = November 25, 2016
 |url-status=live
 |archive-url  = https://web.archive.org/web/20160929205922/http://unesdoc.unesco.org/images/0018/001864/186462e.pdf
 |archive-date = September 29, 2016
 |df          = mdy-all
}}</ref>

When it comes to measuring snow cover on the ground, typically three variables are measured: the snow cover extent (SCE) — the land area covered by snow, snow cover duration (SD) — how long a particular area is covered by snow, and the snow accumulation, often expressed as snow water equivalent (SWE), which expresses how much water the snow would be if it were all melted: this last one is a measurement of the volume of the snowpack.<ref name=":AR6">{{Cite journal |last1=Fox-Kemper |first1=B. |last2=Hewitt |first2=H.T.|author2-link=Helene Hewitt |last3=Xiao |first3=C. |last4=Aðalgeirsdóttir |first4=G. |last5=Drijfhout |first5=S.S. |last6=Edwards |first6=T.L. |last7=Golledge |first7=N.R. |last8=Hemer |first8=M. |last9=Kopp |first9=R.E. |last10=Krinner |first10=G. |last11=Mix |first11=A. |date=2021 |editor-last=Masson-Delmotte |editor-first=V. |editor2-last=Zhai |editor2-first=P. |editor3-last=Pirani |editor3-first=A. |editor4-last=Connors |editor4-first=S.L. |editor5-last=Péan |editor5-first=C. |editor6-last=Berger |editor6-first=S. |editor7-last=Caud |editor7-first=N. |editor8-last=Chen |editor8-first=Y. |editor9-last=Goldfarb |editor9-first=L. |title=Ocean, Cryosphere and Sea Level Change |journal=Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |volume=2021 |publisher=Cambridge University Press, Cambridge, UK and New York, NY, US |pages=1283–1285 |doi=10.1017/9781009157896.011|bibcode=<!-- not 2021AGUFM.U13B..09F --> |isbn=9781009157896 |url=https://www.vliz.be/imisdocs/publications/84/371584.pdf }}</ref> To measure these variables a variety of techniques are used: surface observations, [[remote sensing]], [[Land surface models (climate)|land surface models]] and [[Atmospheric reanalysis|reanalysis products]]. These techniques are often combined to form the most complete datasets.<ref name=":AR6" />

===Satellite data===
[[Remote sensing]] of snowpacks with satellites and other platforms typically includes multi-spectral collection of imagery.<ref>{{cite book |last1=Hall |first1=Dorothy K. |author-link=Dorothy Hall (scientist)|title=Remote Sensing of Ice and Snow |date=1985 |publisher=Springer Netherlands |location=Dordrecht |isbn=978-94-009-4842-6}}</ref> Multi-faceted interpretation of the data obtained allows inferences about what is observed. The science behind these remote observations has been verified with ground-truth studies of the actual conditions.<ref name = Snowenclyclopedia/><ref>{{cite journal |last1=Hall |first1=Dorothy K. |author-link=Dorothy Hall (scientist)|last2=Box |first2=J |last3=Casey |first3=K |last4=Hook |first4=S |last5=Shuman |first5=C |last6=Steffen |first6=K |title=Comparison of satellite-derived and in-situ observations of ice and snow surface temperatures over Greenland |journal=Remote Sensing of Environment |date=15 October 2008 |volume=112 |issue=10 |pages=3739–3749 |doi=10.1016/j.rse.2008.05.007|bibcode=2008RSEnv.112.3739H |hdl=2060/20080030345 |s2cid=91180832 |hdl-access=free }}</ref>

Satellite observations record a decrease in snow-covered areas since the 1960s, when satellite observations began. In some regions such as China, a trend of increasing snow cover was observed from 1978 to 2006. These changes are attributed to global climate change, which may lead to earlier melting and less coverage area. In some areas, snow depth increases because of higher temperatures in latitudes north of 40°. For the Northern Hemisphere as a whole the mean monthly snow-cover extent has been decreasing by 1.3% per decade.<ref name = Review>{{cite journal | author=Dietz, A. |author2=Kuenzer, C. |author3=Gessner, U. |author4= Dech, S. | year=2012 |title=Remote Sensing of Snow – a Review of available methods |journal=International Journal of Remote Sensing |doi=10.1080/01431161.2011.640964|bibcode = 2012IJRS...33.4094D |volume=33 |issue=13 |pages=4094–4134|s2cid=6756253 }}</ref>

The most frequently used methods to map and measure snow extent, snow depth and snow water equivalent employ multiple inputs on the visible–infrared spectrum to deduce the presence and properties of snow. The National Snow and Ice Data Center (NSIDC) uses the reflectance of visible and infrared radiation to calculate a normalized difference snow index, which is a ratio of radiation parameters that can distinguish between clouds and snow. Other researchers have developed decision trees, employing the available data to make more accurate assessments. One challenge to this assessment is where snow cover is patchy, for example during periods of accumulation or ablation and also in forested areas. Cloud cover inhibits optical sensing of surface reflectance, which has led to other methods for estimating ground conditions underneath clouds. For hydrological models, it is important to have continuous information about the snow cover. Passive microwave sensors are especially valuable for temporal and spatial continuity because they can map the surface beneath clouds and in darkness. When combined with reflective measurements, passive microwave sensing greatly extends the inferences possible about the snowpack.<ref name = Review/>

Satellite measurements show that snow cover has been decreasing in many areas of the world since 1978.<ref name=":AR6" />

===Models===
[[File:Watercyclesummary.jpg|thumb|Snowfall and snowmelt are parts of the Earth's water cycle.]]
Snow science often leads to predictive models that include snow deposition, snow melt, and snow hydrology—elements of the Earth's [[water cycle]]—which help describe [[global climate change]].<ref name = Snowenclyclopedia/>

[[Climate model|Global climate change models]] (GCMs) incorporate snow as a factor in their calculations. Some important aspects of snow cover include its [[albedo]] (reflectivity of incident radiation, including light) and insulating qualities, which slow the rate of seasonal melting of sea ice. As of 2011, the melt phase of GCM snow models were thought to perform poorly in regions with complex factors that regulate snow melt, such as vegetation cover and terrain. These models typically derive snow water equivalent (SWE) in some manner from satellite observations of snow cover.<ref name = Snowenclyclopedia/> The ''International Classification for Seasonal Snow on the Ground'' defines SWE as "the depth of water that would result if the mass of snow melted completely".<ref name = Classificationonground/>

Given the importance of snowmelt to agriculture, hydrological runoff models that include snow in their predictions address the phases of accumulating snowpack, melting processes, and distribution of the meltwater through stream networks and into the groundwater. Key to describing the melting processes are solar heat flux, ambient temperature, wind, and precipitation. Initial snowmelt models used a degree-day approach that emphasized the temperature difference between the air and the snowpack to compute snow water equivalent, SWE. More recent models use an energy balance approach that take into account the following factors to compute ''Q<sub>m</sub>'', the energy available for melt. This requires measurement of an array of snowpack and environmental factors to compute six heat flow mechanisms that contribute to ''Q<sub>m</sub>''.<ref name = Snowenclyclopedia/>

==Effects on civilization==
Snow routinely affects civilization in four major areas: transportation, agriculture, structures, and sports. Most transportation modes are impeded by snow on the travel surface. Agriculture often relies on snow as a source of seasonal moisture. Structures may fail under snow loads. Humans find a wide variety of recreational activities in snowy landscapes. It also affects the conduct of warfare.<ref name="chew" />

===Transportation===
{{See also|Snowplow}}
Snow affects the rights of way of highways, airfields and railroads. The [[snowplow]] is common to all workers, though roadways take anti-icing chemicals to prevent bonding of ice and airfields may not; railroads rely on abrasives for track traction.<ref name="FHWA" /><ref name=":1" />

====Highway====
[[File:Cars covered in Snow on Lake Shore Drive Chicago Feb 2 2011 storm.JPG|thumb|Traffic stranded in a [[2011 Groundhog Day blizzard|2011 Chicago snowstorm]].]]
[[File:Snowy Higddhway 4012.jpg|thumb|Reduced visibility on [[Ontario Highway 401]] in Toronto due to a [[snowsquall]].]]
In the late 20th century, an estimated $2 billion was spent annually in North America on roadway winter maintenance, owing to snow and other winter weather events, according to a 1994 report by Kuemmel. The study surveyed the practices of jurisdictions within 44 US states and nine Canadian provinces. It assessed the policies, practices, and equipment used for winter maintenance. It found similar practices and progress to be prevalent in Europe.<ref name = Kuemmel/>

The dominant effect of snow on vehicle contact with the road is diminished friction. This can be improved with the use of [[snow tire]]s, which have a tread designed to compact snow in a manner that enhances traction. The key to maintaining a roadway that can accommodate traffic during and after a snow event is an effective anti-icing program that employs both chemicals and [[Snowplow|plowing]].<ref name = Kuemmel>{{cite book|url=https://books.google.com/books?id=I3gxuwTE5_MC&pg=PA10|title=Managing roadway snow and ice control operations|author=David A. Kuemmel|page=10|isbn=978-0-309-05666-3|publisher=Transportation Research Board|year=1994|access-date=July 8, 2009}}</ref> The [[Federal Highway Administration]] ''Manual of Practice for an Effective Anti-icing Program'' emphasizes "anti-icing" procedures that prevent the bonding of snow and ice to the road. Key aspects of the practice include: understanding anti-icing in light of the level of service to be achieved on a given roadway, the climatic conditions to be encountered, and the different roles of deicing, anti-icing, and abrasive materials and applications, and employing anti-icing "toolboxes", one for operations, one for decision-making and another for personnel. The elements to the toolboxes are:<ref name=FHWA>
{{cite web
 |url         = https://www.fhwa.dot.gov/reports/mopeap/mop0296a.htm#eapappa2
 |title       = Manual of Practice for an Effective Anti-icing Program: A Guide For Highway Winter Maintenance Personnel
 |last1        = Ketcham
 |first1       = Stephen A.
 |last2       = Minsk
 |first2      = L. David
 |display-authors=2
 |author3=Robert R. Blackburn
 |author4=Edward J. Fleege
 |date        = June 1995
 |website     = [[Federal Highway Administration|Federal Highway Administration (FHWA)]]
 |publisher   = FHWA
 |access-date = December 1, 2016
 |quote       = Highway anti-icing is the snow and ice control practice of preventing the formation or development of bonded snow and ice by timely applications of a chemical freezing-point depressant.
 |url-status=live
 |archive-url  = https://web.archive.org/web/20161201084330/http://www.fhwa.dot.gov/reports/mopeap/mop0296a.htm#eapappa2
 |archive-date = December 1, 2016
 |df          = mdy-all
}}</ref>
* ''Operations'' – Addresses the application of solid and liquid chemicals, using various techniques, including prewetting of chloride-salts. It also addresses plowing capability, including types of snowplows and blades used.
* ''Decision-making'' – Combines weather forecast information with road information to assess the upcoming needs for application of assets and the evaluation of treatment effectiveness with operations underway.
* ''Personnel'' – Addresses training and deployment of staff to effectively execute the anti-icing program, using the appropriate materials, equipment and procedures.
The manual offers matrices that address different types of snow and the rate of snowfall to tailor applications appropriately and efficiently.

[[Snow fence]]s, constructed upwind of roadways control snow drifting by causing windblown, drifting snow to accumulate in a desired place. They are also used on railways. Additionally, farmers and ranchers use snow fences to create drifts in basins for a ready supply of water in the spring.<ref>{{Citation| first1 =R| last1 =Jairell| first2 =R| last2 =Schmidt| title =Snow Management and Windbreaks| contribution =133| series =Range Beef Cow Symposium| year =1999| pages =12| publisher =[[University of Nebraska–Lincoln]]| url =http://www1.foragebeef.ca/$Foragebeef/frgebeef.nsf/all/frg4952/$FILE/snow_mgmt.pdf| url-status=live| archive-url =https://web.archive.org/web/20160507023359/http://www1.foragebeef.ca/$Foragebeef/frgebeef.nsf/all/frg4952/$FILE/snow_mgmt.pdf| archive-date =May 7, 2016| df =mdy-all}}</ref><ref>{{cite journal|url=https://www.sciencedaily.com/releases/2009/01/090129113327.htm|title='SnowMan' Software Helps Keep Snow Drifts Off The Road|date=February 6, 2009|journal=ScienceDaily|access-date=July 12, 2009|url-status=live|archive-url=https://web.archive.org/web/20090416122409/https://www.sciencedaily.com/releases/2009/01/090129113327.htm|archive-date=April 16, 2009|df=mdy-all}}</ref>

====Aviation====
{{See also|Ice protection system}}
[[File:2008 aircraft deicing at gate.jpg|thumb|right|Deicing an aircraft during a snow event]]
In order to keep airports open during winter storms, runways and taxiways require snow removal. Unlike roadways, where chloride chemical treatment is common to prevent snow from bonding to the pavement surface, such chemicals are typically banned from airports because of their strong corrosive effect on aluminum aircraft. Consequently, mechanical brushes are often used to complement the action of snow plows. Given the width of runways on airfields that handle large aircraft, vehicles with large plow blades, an echelon of plow vehicles or [[rotary snowplow]]s are used to clear snow on runways and taxiways. Terminal aprons may require {{convert|6|ha}} or more to be cleared.<ref name=Vinson>
{{Citation
 |first1            = Becker
 |last1             = John C.
 |first2           = David C.
 |last2            = Esch
 |editor-last      = Vinson
 |editor-first     = Ted S.
 |editor2-last     = Rooney
 |editor2-first    = James W.
 |editor3-last     = Haas
 |editor3-first    = Wilbur H.
 |title            = Roads and Airfields in Cold Regions: A State of the Practice Report
 |contribution     = Road and airfield maintenance
 |series           = CERF Reports
 |year             = 1996
 |page             = 252
 |publisher        = ASCE Publications
 |url              = https://books.google.com/books?id=VfO8QuV0q0sC&pg=PA252
 |isbn             = 978-0-7844-7412-9
 }}</ref>

Properly equipped aircraft are able to fly through snowstorms under [[instrument flight rules]]. Prior to takeoff, they require [[deicing fluid]] during snowstorms to prevent accumulation and freezing of snow and other precipitation on wings and fuselages, which may compromise the safety of the aircraft and its occupants.<ref>Transport Canada, Ottawa, ON (2016). [http://www.tc.gc.ca/eng/civilaviation/publications/tp14052-chapter8-312.htm "TP 14052. Guidelines for Aircraft Ground-Icing Operations. Chapter 8. Fluids."] {{webarchive|url=https://web.archive.org/web/20140527220255/http://www.tc.gc.ca/eng/civilaviation/publications/tp14052-chapter8-312.htm |date=May 27, 2014 }} Retrieved May 14, 2016.</ref> In flight, aircraft rely on a variety of mechanisms to avoid rime and other types of icing in clouds,<ref>
{{cite web
 | url = http://www.airspacemag.com/how-things-work/electro-mechanical-deicing-6660440/
 | title = Electro-mechanical deicing
 | last = Wright
 | first = Tim
 | date = March 2004
 | website = Air & Space Magazine
 | publisher = Smithsonian
 | access-date = February 20, 2017
 }}</ref> these include pulsing [[deicing boot|pneumatic boots]], electro-thermal areas that generate heat, and fluid deicers that bleed onto the surface.<ref>{{cite web
 |url         = https://www.aopa.org/-/media/files/aopa/home/pilot-resources/asi/safety-advisors/sa22.pdf?la=en
 |title       = Aircraft Deicing and Anti-icing Equipment
 |last        = Ells
 |first       = Steve
 |date        = 2004
 |website     = Safety Advisor – Weather No. 2
 |publisher   = Aircraft Owners and Pilots Association
 |access-date = December 1, 2016
 |quote       = Anti-icing equipment is turned on before entering icing conditions and is designed to prevent ice from forming. Deicing equipment is designed to remove ice after it begins to accumulate on the airframe.
 |url-status=live
 |archive-url  = https://web.archive.org/web/20161203000432/https://www.aopa.org/-/media/files/aopa/home/pilot-resources/asi/safety-advisors/sa22.pdf?la=en
 |archive-date = December 3, 2016
 |df          = mdy-all
}}</ref>

====Rail====
Railroads have traditionally employed two types of snow plows for clearing track: the [[wedge plow]], which casts snow to both sides, and the [[rotary snowplow]], which is suited for addressing heavy snowfall and casting snow far to one side or the other. Prior to the invention of the rotary snowplow ca. 1865, it required multiple [[locomotive]]s to drive a wedge plow through deep snow. After clearing the track with such plows, a "flanger" is used to clear snow from between the rails that are below the reach of the other types of plows. Where icing may affect the steel-to-steel contact of locomotive wheels on track, abrasives (typically sand) have been used to provide traction on steeper uphills.<ref name=":1">
{{cite book
 | last = Bianculli
 | first = Anthony J.
 | title = The American Railroad in the Nineteenth Century – Cars
 | publisher = University of Delaware Press
 | series = Trains and Technology
 | volume = 2
 | date = 2001
 | location = Dover
 | page = 170
 | url = https://books.google.com/books?id=2fh0H0USx-0C&pg=PA170
 | access-date = December 2, 2016
 | isbn = 978-0-87413-730-9 }}</ref>

Railroads employ [[snow shed]]s—structures that cover the track—to prevent the accumulation of heavy snow or avalanches to cover tracks in snowy mountainous areas, such as the [[Alps]] and the [[Rocky Mountains]].<ref>{{cite web
 |url         = http://www.fao.org/docrep/x5376e/x5376e04.htm
 |title       = Avalanche and torrent control in the Spanish Pyrenees
 |last        = FAO
 |first       = Staff
 |website     = National Forests Organization of Spain
 |publisher   = Patrimonio Forestal del Estado
 |access-date = December 1, 2016
 |url-status=live
 |archive-url  = https://web.archive.org/web/20150924140432/http://www.fao.org/docrep/x5376e/x5376e04.htm
 |archive-date = September 24, 2015
 |df          = mdy-all
}}</ref>
<gallery caption="Snowplows for different transportation modes" mode="packed" heights="150px">
File:TowPLow front view2.JPG|Trucks plowing snow on a highway in [[Missouri]]
File:Winter Operations @ Brussels Airport January 2013 (8387468508).jpg|Airport snow-clearing operations include plowing and brushing
File:RhB ABe 8-12 Allegra mit Spurpflug bei Ospizio Bernina.jpg|Swiss low-profile, train-mounted snowplow
</gallery>

====Construction====
Snow can be compacted to form a [[snow road]] and be part of a [[Winter road|winter road route]] for vehicles to access isolated communities or construction projects during the winter.<ref name = Abele>Abele, G., 1990. Snow roads and runways, U.S. Army Cold Regions Research and Engineering Laboratory, Monograph 90-3, Washington, D.C.</ref> Snow can also be used to provide the supporting structure and surface for a runway, as with the [[Phoenix Airfield]] in Antarctica. The snow-compacted runway is designed to withstand approximately 60 wheeled flights of heavy-lift military aircraft a year.<ref name="usap4212">{{cite web| url=http://www.usap.gov/News/contentHandler.cfm?id=4212| title=A New Runway for McMurdo Station is Named| publisher=National Science Foundation| date=7 April 2016| url-status=live| archive-url=https://web.archive.org/web/20160423090553/http://www.usap.gov/News/contentHandler.cfm?id=4212| archive-date=April 23, 2016| df=mdy-all}}</ref>

===Agriculture===
[[File:Indus.A2002274.0610.1km.jpg|thumb|Satellite view of the [[Indus River Basin]], showing snow in the mountain ranges—including the Himalayas—which feed the Indus river and its tributaries, and agricultural areas in eastern [[Pakistan]] and northwestern [[India]] that draw on them for irrigation.]]
Snowfall can be beneficial to agriculture by serving as a [[thermal insulation|thermal insulator]], conserving the heat of the Earth and protecting [[agriculture|crops]] from subfreezing weather. Some agricultural areas depend on an accumulation of snow during winter that will melt gradually in spring, providing water for crop growth, both directly and via runoff through streams and rivers, which supply irrigation canals.<ref name = Snowenclyclopedia/> The following are examples of rivers that rely on meltwater from glaciers or seasonal snowpack as an important part of their flow on which irrigation depends: the [[Ganges]], many of whose tributaries rise in the [[Himalayas]] and which provide much irrigation in northeast [[India]],<ref>{{cite book
 |first1      = C. R.
 |last1       = Krishna Murti
 |others      = Gaṅgā Pariyojanā Nideśālaya; India Environment Research Committee
 |title       = The Ganga, a scientific study
 |date        = 1991
 |publisher   = Northern Book Centre
 |isbn        = 978-8172110215
 |df          = mdy-all
|oclc       = 853267663
 }}</ref> the [[Indus River]], which rises in [[Tibet]]<ref>[[Alice Albinia|Albinia, Alice]]. (2008) ''Empires of the Indus: The Story of a River''. First American Edition (20101) W. W. Norton & Company, New York. {{ISBN|978-0-393-33860-7}}.</ref> and provides irrigation water to [[Pakistan]] from rapidly retreating Tibetan glaciers,<ref>{{cite web |url=https://www.google.com/hostednews/afp/article/ALeqM5g1eE4Xw3njaW1MKpJRYOch4hOdLQ |title=Global warming benefits to Tibet: Chinese official. Reported 18 August 2009 |date=August 17, 2009 |access-date=December 4, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20100123192540/https://www.google.com/hostednews/afp/article/ALeqM5g1eE4Xw3njaW1MKpJRYOch4hOdLQ |archive-date=January 23, 2010 |df=mdy-all }}</ref> and the [[Colorado River]], which receives much of its water from seasonal snowpack in the [[Rocky Mountains]]<ref name="USGSrivers">{{cite web|url=http://pubs.usgs.gov/of/1987/ofr87-242/|author=Kammerer, J.C.|title=Largest Rivers in the United States|publisher=U.S. Geological Survey|date=May 1990|access-date=July 2, 2010|url-status=live|archive-url=https://web.archive.org/web/20170129040848/https://pubs.usgs.gov/of/1987/ofr87-242/|archive-date=January 29, 2017|df=mdy-all}}</ref> and provides irrigation water to some {{convert|4|e6acre|e6ha|abbr=off}}.<ref>{{cite web|url=http://www.usbr.gov/newsroom/newsrelease/detail.cfm?RecordID=38043|title=Salazar Awards $20.1 Million to Four Western Colorado Irrigation Districts to Improve Irrigation Systems, Reduce Salinity in Colorado River|publisher=U.S. Bureau of Reclamation|date=October 21, 2011|access-date=March 17, 2012|url-status=dead|archive-url=https://web.archive.org/web/20111030103029/http://www.usbr.gov/newsroom/newsrelease/detail.cfm?RecordID=38043|archive-date=October 30, 2011|df=mdy-all}}</ref>

===Structures===
[[File:Snow in Grindelwald.jpg|thumb|right|Extreme snow accumulation on building roofs]]
Snow is an important consideration for loads on structures. To address these, European countries employ ''Eurocode 1: Actions on structures - Part 1-3: General actions - Snow loads''.<ref name=Eurocode1>
{{Citation
 | author = Joint European Commission
 | title = General actions - Snow loads
 | journal = Eurocode 1
 | volume = EN 1991-1-3:2003
 | issue = Actions on structures - Part 1–3
 | year = 2003
 | url = http://eurocodes.jrc.ec.europa.eu/showpage.php?id=131 }}</ref> In North America, ASCE ''Minimum Design Loads for Buildings and Other Structures'' gives guidance on snow loads.<ref name=ASCE7>
{{Citation
 |author      = Committee on Minimum Design Loads for Buildings
 |title       = Minimum Design Loads for Buildings and Other Structures
 |issue       = ASCE 7–10
 |pages       = 636
 |year        = 2013
 |url         = https://law.resource.org/pub/us/cfr/ibr/003/asce.7.2002.pdf
 |publisher   = American Society of Civil Engineers
 |access-date = December 2, 2016
 |isbn        = 9780784413227
 |url-status=live
 |archive-url  = https://web.archive.org/web/20161011024914/https://law.resource.org/pub/us/cfr/ibr/003/asce.7.2002.pdf
 |archive-date = October 11, 2016
 |df          = mdy-all
}}</ref> Both standards employ methods that translate maximum expected ground snow loads onto design loads for roofs.{{cn|date=May 2025}}

====Roofs====
[[File:Ice dam and roof leakage.jpg|thumb|right|Icings resulting from meltwater at the bottom of the snow pack on the roof, flowing and refreezing at the eave as icicles and from leaking into the wall via an ice dam.]]
Snow loads and icings are two principal issues for roofs. Snow loads are related to the climate in which a structure is sited. Icings are usually a result of the building or structure generating heat that melts the snow that is on it.{{cn|date=May 2025}}

''Snow loads'' – The ''Minimum Design Loads for Buildings and Other Structures'' gives guidance on how to translate the following factors into roof snow loads:<ref name = ASCE7/>
* Ground snow loads
* Exposure of the roof
* Thermal properties of the roof
* Shape of the roof
* Drifting
* Importance of the building
It gives tables for ground snow loads by region and a methodology for computing ground snow loads that may vary with elevation from nearby, measured values. The ''Eurocode 1'' uses similar methodologies, starting with ground snow loads that are tabulated for portions of Europe.<ref name=Eurocode1/>

''Icings'' – Roofs must also be designed to avoid [[Ice dam (roof)|ice dams]], which result from meltwater running under the snow on the roof and freezing at the eave. Ice dams on roofs form when accumulated snow on a sloping roof melts and flows down the roof, under the insulating blanket of snow, until it reaches below freezing temperature air, typically at the [[eaves]]. When the meltwater reaches the freezing air, ice accumulates, forming a dam, and snow that melts later cannot drain properly through the dam.<ref name="Paul" >Paul Fisette, "Preventing Ice Dams", ''Roofing, flashing & waterproofing''. Newtown, CT: Taunton Press, 2005. 54.</ref> Ice dams may result in [[Water damage|damaged]] building materials or in damage or injury when the ice dam falls off or from attempts to remove ice dams. The melting results from heat passing through the roof under the highly insulating layer of snow.<ref>{{citation| url=http://www.state.mn.us/portal/mn/jsp/content.do?test=y&id=-536881350&subchannel=-536881511&sc2=null&sc3=null&contentid=536884951&contenttype=EDITORIAL&programid=536886479&agency=Commerce|title=Ice Dams|publisher=Minnesota Department of Commerce|archive-url=https://web.archive.org/web/20070824154322/http://www.state.mn.us/portal/mn/jsp/content.do?test=y&id=-536881350&subchannel=-536881511&sc2=null&sc3=null&contentid=536884951&contenttype=EDITORIAL&programid=536886479&agency=Commerce| archive-date=August 24, 2007}}</ref><ref name="Hansen" >
{{Citation
 | first1 = I.
 | last1 = MacKinley
 | first2 = R.
 | last2 = Flood
 | first3 = A.
 | last3 = Heidrich
 | editor-last = Hjorth-Hansen
 | editor-first = E.
 | editor2-last = Holand
 | editor2-first = I.
 | editor3-last = Loset
 | editor3-first = S.
 | editor4-last = Norem
 | editor4-first = H.
 | contribution = Roof design in regions of snow and cold
 | isbn = 9789058091482
 | title = Snow Engineering 2000: Recent Advances and Developments
 | year = 2000
 | pages = 470
 | place = Rotterdam
 | publisher = CRC Press
 | url = https://books.google.com/books?id=EjGsPSoYHOIC
}}</ref>

====Utility lines====
In areas with trees, utility distribution lines on poles are less susceptible to snow loads than they are subject to damage from trees falling on them, felled by heavy, wet snow.<ref>
{{cite web
 |url         = https://www.progress-energy.com/carolinas/home/safety-information/storm-safety-tips/outages.page?
 |title       = Storms & Outages
 |last        = Technical staff
 |date        = 2015
 |publisher   = Duke Energy
 |access-date = December 6, 2016
 |quote       = Both snow and ice cause power outages primarily by weighing down tree limbs and power lines, causing them to break
 |url-status=dead
 |archive-url  = https://web.archive.org/web/20161220104742/https://www.progress-energy.com/carolinas/home/safety-information/storm-safety-tips/outages.page
 |archive-date = December 20, 2016
 |df          = mdy-all
}}</ref> Elsewhere, snow can accrete on power lines as "sleeves" of rime ice. Engineers design for such loads, which are measured in kg/m (lb/ft) and power companies have forecasting systems that anticipate types of weather that may cause such accretions. Rime ice may be removed manually or by creating a sufficient short circuit in the affected segment of power lines to melt the accretions.<ref>{{Citation
 | last = Farzaneh
 | first = Masoud
 | title = Atmospheric Icing of Power Networks
 | publisher = Springer Science & Business Media
 | year = 2008
 | page = 141
 | url = https://books.google.com/books?id=Ufg-AAAAQBAJ&pg=PA141
 | isbn = 9781402085314 }}</ref><ref>{{Citation
 |last1            = Bonelli
 |first1           = P.
 |last2           = Lacavalla
 |first2          = M.
 |display-authors = etal <!--P. Marcacci, G. Mariani, and G. Stella-->
 |title           = Wet snow hazard for power lines: a forecast and alert system applied in Italy
 |journal         = Natural Hazards and Earth System Sciences
 |volume          = 11
 |issue           = 9
 |year            = 2011
 |pages           = 2419–2431
 |doi             = 10.5194/nhess-11-2419-2011
 |bibcode         = 2011NHESS..11.2419B
 |s2cid = 15569449
 |df              = mdy-all
|doi-access= free
 }}</ref>

===Sports and recreation===
[[File:Ski Famille - Family Ski Holidays.jpg|thumb|Alpine skiing]]
{{Main|Winter sport}}
Snow figures into many winter sports and forms of recreation, including [[skiing]] and [[sledding]]. Common examples include [[cross-country skiing]], [[Alpine skiing]], [[snowboarding]], [[snowshoe]]ing, and [[Snowmobile|snowmobiling]]. The design of the equipment used, e.g. skis and snowboards, typically relies on the bearing strength of snow and contends with the [[coefficient of friction]] bearing on snow.<ref name="Colbeck">{{Citation |last=Colbeck |first=Samuel C. |title=A Review of the Processes That Control Snow Friction |date=April 1992 |journal=CRREL Monograph |volume=92 |issue=2 |pages=49 |url=http://acwc.sdp.sirsi.net/client/en_US/search/asset/1011800 |access-date=2016-01-19 |archive-url=https://web.archive.org/web/20160126095240/http://acwc.sdp.sirsi.net/client/en_US/search/asset/1011800 |archive-date=2016-01-26 |url-status=dead}}</ref>

Skiing is by far the largest form of winter recreation. As of 1994, of the estimated 65–75 million skiers worldwide, there were approximately 55 million who engaged in [[Alpine skiing]], the rest engaged in [[cross-country skiing]]. Approximately 30 million skiers (of all kinds) were in Europe, 15 million in the US, and 14 million in Japan. As of 1996, there were reportedly 4,500 ski areas, operating 26,000 ski lifts and enjoying 390 million skier visits per year. The preponderant region for downhill skiing was Europe, followed by Japan and the US.<ref>
{{cite book
 | last = Hudson
 | first = Simon
 | title = Snow Business: A Study of the International Ski Industry
 | publisher = Cengage Learning EMEA
 | series = Tourism (Cassell)
 | date = 2000
 | pages = 180
 | url = https://books.google.com/books?id=tGRLt8tG-kMC&pg=PA27
 | isbn = 9780304704712}}</ref>

Increasingly, ski resorts are relying on [[snowmaking]], the production of snow by forcing water and pressurized air through a [[Snowmaking#Snowmaking guns|snow gun]] on ski slopes.<ref>{{US patent reference|number=2676471|inventor=W. M. Pierce Jr.|title=Method for Making and Distributing Snow|issue-date=December 14, 1950}}</ref> Snowmaking is mainly used to supplement natural snow at [[ski resort]]s.<ref>[http://news.bbc.co.uk/onthisday/hi/dates/stories/march/25/newsid_2786000/2786871.stm On This Day: March 25] {{webarchive|url=https://web.archive.org/web/20110412010130/http://news.bbc.co.uk/onthisday/hi/dates/stories/march/25/newsid_2786000/2786871.stm |date=April 12, 2011 }}, [[BBC News]], accessed December 20, 2006. "The first artificial snow was made two years later, in 1952, at Grossinger's resort in New York, USA. "</ref> This allows them to improve the reliability of their snow cover and to extend their ski seasons from late autumn to early spring. The production of snow requires low temperatures. The threshold temperature for snowmaking increases as humidity decreases. [[Wet-bulb temperature]] is used as a metric since it takes air temperature and relative humidity into account. Snowmaking is a relatively expensive process in its energy consumption, thereby limiting its use.<ref>{{citation|url=http://bachler.cms1.ch/Portals/41/docs/energy_usage_for_snowmaking.pdf|title=Energy usage for snowmaking|author=Jörgen Rogstam|author2=Mattias Dahlberg|name-list-style=amp|date=April 1, 2011|url-status=live|archive-url=https://web.archive.org/web/20140201200900/http://bachler.cms1.ch/Portals/41/docs/energy_usage_for_snowmaking.pdf|archive-date=February 1, 2014|df=mdy-all}}</ref>

[[Ski wax]] enhances the ability of a ski (or other runner) to slide over snow by reducing its coefficient of friction, which depends on both the properties of the snow and the ski to result in an optimum amount of lubrication from melting the snow by friction with the ski—too little and the ski interacts with solid snow crystals, too much and capillary attraction of meltwater retards the ski. Before a ski can slide, it must overcome the maximum value static friction. Kinetic (or dynamic) friction occurs when the ski is moving over the snow.<ref name="Bhavikatti">{{cite book
| url = https://books.google.com/books?id=4wkLl4NvmWAC&pg=PA112
| title = Engineering Mechanics
| last = Bhavikatti
| first = S. S.
|author2=K. G. Rajashekarappa
| page = 112
| access-date = October 21, 2007
| publisher = New Age International
| isbn = 978-81-224-0617-7
| year = 1994}}</ref>

===Warfare===
{{main|Cold-weather warfare}}
{{see also|Ski warfare}}
Snow affects warfare conducted in winter, alpine environments or at high latitudes. The main factors are ''impaired visibility'' for acquiring targets during falling snow, ''enhanced visibility'' of targets against snowy backgrounds for targeting, and mobility for both [[Mechanized infantry|mechanized]] and [[infantry]] troops. Snowfall can severely inhibit the [[Military logistics|logistics of supplying troops]], as well. Snow can also provide cover and fortification against small-arms fire.<ref name=chew>{{cite journal
 |last        = Chew
 |first       = Allen F.
 |title       = Fighting the Russians in Winter: Three Case Studies
 |journal     = Leavenworth Papers
 |issue       = 5
 |place       = Fort Leavenworth, Kansas
 |date        = December 1981
 |url         = http://www.cgsc.edu/carl/download/csipubs/chew.pdf
 |issn        = 0195-3451
 |access-date = December 10, 2016
 |url-status=dead
 |archive-url  = https://web.archive.org/web/20111013030919/http://cgsc.edu/carl/download/csipubs/chew.pdf
 |archive-date = October 13, 2011
 |df          = mdy-all
}}</ref> Noted [[winter warfare]] campaigns where snow and other factors affected the operations include:
* The [[French invasion of Russia]], where poor traction conditions for ill-shod horses made it difficult for supply wagons to keep up with troops.<ref>{{cite news |url=https://www.bbc.co.uk/news/magazine-16929522 |title=Napoleon's failure: For the want of a winter horseshoe |work=BBC News magazine |author=Professor Saul David |date=February 9, 2012 |access-date=February 9, 2012 |url-status=live |archive-url=https://web.archive.org/web/20120209074411/http://www.bbc.co.uk/news/magazine-16929522 |archive-date=February 9, 2012 |df=mdy-all }}</ref> That campaign was also strongly affected by cold, whereby the retreating army reached [[Neman River]] in December 1812 with only 10,000 of the 420,000 that had set out to invade [[Russia]] in June of the same year.<ref name="The Wordsworth Pocket Encyclopedia p. 17">The Wordsworth Pocket Encyclopedia, p. 17, Hertfordshire 1993.</ref>
* The [[Winter War]], an attempt by the [[Soviet Union]] to take territory in [[Finland]] in late 1939 demonstrated superior winter tactics of the [[Finnish Army]], regarding over-snow mobility, [[camouflage]], and use of the terrain.<ref name="Clemmesen">{{cite book |editor1-last=Clemmesen |editor1-first=Michael H. |editor2-last=Faulkner |editor2-first=Marcus |title=Northern European Overture to War, 1939–1941: From Memel to Barbarossa| year=2013 |publisher=Brill |page=76 |isbn=978-90-04-24908-0}}</ref>
* The [[Battle of the Bulge]], a German counteroffensive during [[World War II]], starting December 16, 1944, was marked by heavy snowstorms that hampered allied air support for ground troops, but also impaired German attempts to supply their front lines.<ref>{{citation |last=Parker |first=Danny S. |title=Battle of the Bulge: Hitler's Ardennes Offensive, 1944–1945 |publisher=Combined Books |year=1991 |isbn=978-0-938289-04-3}}</ref> On the Eastern Front with the Nazi invasion of Russia in 1941, [[Operation Barbarossa]], both Russian and German soldiers had to endure terrible conditions during the [[Russian winter]]. While use of [[ski infantry]] was common in the Red Army, Germany formed only [[1st Ski Division (Germany)|one division]] for movement on skis.<ref name="Clemmesen"/>
* The [[Korean War]] which lasted from June 25, 1950, until an armistice on July 27, 1953, began when [[North Korea]] invaded [[South Korea]]. Much of the fighting occurred during winter conditions, involving snow,<ref>{{cite book
| last = Halberstam
| first = David
| author-link = David Halberstam
| year = 2007
| title = The Coldest Winter: America and the Korean War
| publisher = Hyperion
| location = New York
| isbn = 978-1-4013-0052-4
| title-link = The Coldest Winter: America and the Korean War
}}</ref> notably during the [[Battle of Chosin Reservoir]], which was a stark example of cold affecting military operations, especially vehicles and weapons.<ref>
{{cite book
 | last = Tilstra
 | first = Russell C.
 | title = The Battle Rifle: Development and Use Since World War II
 | publisher = McFarland
 | date = 2014
 | page = 28
 | url = https://books.google.com/books?id=_a0zAwAAQBAJ&pg=PA28
 | isbn = 978-1-4766-1564-6 }}</ref>
<gallery caption="Military operations in snow" mode="packed" heights="150px">
File:Night Bivouac of Great Army.jpg|Bivouac of [[Napoleon]]'s [[Grande Armée]], during the winter retreat from [[Moscow]]
File:Finn ski troops.jpg|Finnish ski troops during the invasion of [[Finland]] by the [[Soviet Union]]
File:Army vehicles on a road in Belgium.jpg|Army vehicles coping with snow during the [[Battle of the Bulge]] of [[World War II]]
File:Cold Response DV dag.jpg|Norwegian military preparations during the 2009 [[Cold Response]] exercise
File:Navy Seals Winter warfare at Mammoth Mountain, California, in December 2014.jpg|[[United States Navy SEALs]] training for winter warfare at [[Mammoth Mountain]], [[California]]
</gallery>

==Effects on plants and animals==
[[File:Chlamydomonas nivalis.jpg|thumb|right|Algae, ''[[Chlamydomonas nivalis]]'', that thrive in snow form red areas in the [[Suncup (snow)|suncups]] on this snow surface]]
Plants and animals endemic to snowbound areas develop ways to adapt. Among the adaptive mechanisms for plants are freeze-adaptive chemistry,<ref>{{Cite book |last1=Gusta |first1=Lawrence V. |url=https://books.google.com/books?id=ZWEpyNDefGkC&dq=plant+antifreeze&pg=PA26 |title=Plant Cold Hardiness: From the Laboratory to the Field |last2=Tanino |first2=Karen K. |last3=Wisniewski |first3=Michael E. |date=2009 |publisher=CABI |isbn=978-1-84593-513-9 |pages=19–27 |language=en}}</ref> dormancy, seasonal dieback, survival of seeds; and for animals are hibernation, insulation, anti-freeze chemistry, storing food, drawing on reserves from within the body, and clustering for mutual heat.<ref name = SnowEcology/>

Snow interacts with vegetation in two principal ways: vegetation can influence the deposition and retention of snow and, conversely, the presence of snow can affect the distribution and growth of vegetation. Tree branches, especially of [[conifer]]s intercept falling snow and prevent accumulation on the ground. Snow suspended in trees ablates more rapidly than that on the ground, owing to its greater exposure to sun and air movement. Trees and other plants can also promote snow retention on the ground, which would otherwise be blown elsewhere or melted by the sun. Snow affects vegetation in several ways, the presence of stored water can promote growth, yet the annual onset of growth is dependent on the departure of the snowpack for those plants that are buried beneath it. Furthermore, avalanches and erosion from snowmelt can scour terrain of vegetation.<ref name = Snowenclyclopedia/>

[[File:Fjellrev - Arctic fox (24490250823).jpg|thumb|right|[[Arctic fox]], a predator of smaller animals that live beneath the snow]]
Snow supports a wide variety of animals both on the surface and beneath. Many [[invertebrate]]s thrive in snow, including [[spider]]s, [[wasp]]s, [[beetle]]s, [[snow scorpionflies]] and [[springtail]]s. Such [[arthropod]]s are typically active at temperatures down to {{convert|-5|C}}. Invertebrates fall into two groups, regarding surviving subfreezing temperatures: freezing-resistant and those that avoid freezing because they are freeze-sensitive. The first group may be cold hardy owing to the ability to produce [[antifreeze]] agents in their body fluids that allows survival of long exposure to sub-freezing conditions. Some organisms [[Fasting|fast]] during the winter, which expels freezing-sensitive contents from their digestive tracts. The ability to survive the absence of oxygen in ice is an additional survival mechanism.<ref name = SnowEcology/>

Small [[vertebrates]] are active beneath the snow. Among vertebrates, [[alpine salamander]]s are active in snow at temperatures as low as {{convert|-8|C}}; they burrow to the surface in springtime and lay their eggs in melt ponds. Among mammals, those that remain active are typically smaller than {{convert|250|g}}. [[Omnivore]]s are more likely to enter a torpor or be [[Hibernate|hibernators]], whereas [[herbivore]]s are more likely to maintain food caches beneath the snow. [[Vole]]s store up to {{convert|3|kg}} of food and [[pika]]s up to {{convert|20|kg}}. Voles also huddle in communal nests to benefit from one another's warmth. On the surface, [[wolves]], [[coyotes]], [[fox]]es, [[lynx]], and [[weasel]]s rely on these subsurface dwellers for food and often dive into the snowpack to find them.<ref name = SnowEcology>
{{cite book
 | last = Jones
 | first = H. G.
 | title = Snow Ecology: An Interdisciplinary Examination of Snow-Covered Ecosystems
 | publisher = Cambridge University Press
 | date = 2001
 | page = 248
 | url = https://books.google.com/books?id=2GzOeAA7vucC&pg=PA248
 | isbn = 978-0-521-58483-8 }}</ref>

== Outside of Earth ==
Extraterrestrial "snow" includes water-based precipitation, but also precipitation of other compounds prevalent on other planets and moons in the [[Solar System]]. Examples are:
* On [[Mars]], observations of the [[Phoenix (spacecraft)|''Phoenix'' Mars lander]] revealed that water-based snow crystals occur at high latitudes.<ref>{{cite web|url=http://news.nationalgeographic.com/news/2009/07/090702-snow-mars-phoenix.html|title="Diamond Dust" Snow Falls Nightly on Mars|author=Anne Minard|date=July 2, 2009|publisher=[[National Geographic News]]|url-status=dead|archive-url=https://web.archive.org/web/20090917075510/http://news.nationalgeographic.com/news/2009/07/090702-snow-mars-phoenix.html|archive-date=September 17, 2009|df=mdy-all}}</ref> Additionally, [[carbon dioxide]] precipitates from clouds during the Martian winters at the poles and contributes to a seasonal deposit of that compound, which is the principal component of that [[Martian polar ice caps|planet's ice caps]].<ref>{{cite web
|url = http://www.spaceref.com/news/viewpr.html?pid=26493
|title = Mars polar cap mystery solved
|last = Agustin Chicarro
|first = Agustin
|date = September 22, 2008
|website = Spaceref.com
|publisher = [[European Space Agency]]
|access-date = December 8, 2016
|quote = ...the temperature of the low-pressure system is often below the condensation point for carbon dioxide, so the gas condenses and falls from the sky as snow and builds up on the ground as frost.
|archive-date = March 7, 2023
|archive-url = https://web.archive.org/web/20230307035744/https://spaceref.com/press-release/mars-polar-cap-mystery-solved/
|url-status = dead
}}</ref>
* On [[Venus]], observations from the [[Magellan (spacecraft)|''Magellan'' spacecraft]] revealed the presence a metallic substance, which precipitates as "[[Venus snow]]" and leaves a highly reflective substance at the tops of Venus's highest mountain peaks resembling terrestrial snow. Given the high temperatures on Venus, the leading candidates for the precipitate are [[lead sulfide]] and [[bismuth(III) sulfide]].<ref>{{cite web
|title       = 'Heavy metal' snow on Venus is lead sulfide
|author      = Carolyn Jones Otten
|publisher   = Washington University in St Louis
|url         = http://news-info.wustl.edu/news/page/normal/633.html
|year        = 2004
|access-date  = August 21, 2007
|url-status=live
|archive-url  = https://web.archive.org/web/20080415000214/http://news-info.wustl.edu/news/page/normal/633.html
|archive-date = April 15, 2008
|df          = mdy-all
}}</ref>
* On [[Saturn]]'s moon, [[Titan (moon)|Titan]], [[Cassini–Huygens|''Cassini–Huygens'' spacecraft]] observations suggested the presence of [[methane]] or some other form of [[hydrocarbon]]-based crystalline deposits.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/cassini/media/cassini-20061212.html|title=Massive Mountain Range Imaged on Saturn's Moon Titan|publisher=[[NASA]]|author=Carolina Martinez|date=December 12, 2006|url-status=live|archive-url=https://web.archive.org/web/20160304072221/http://www.nasa.gov/mission_pages/cassini/media/cassini-20061212.html|archive-date=March 4, 2016|df=mdy-all}}</ref>
* On [[Pluto]], [[New Horizons]]' observations showed that methane condenses at high altitude and falls down as frost.<ref>{{Cite web|date=2016-03-05|title=Methane Snow on Pluto's Peaks {{!}} NASA|work=NASA |url=https://www.nasa.gov/feature/methane-snow-on-pluto-s-peaks/|access-date=2024-09-26|archive-url=https://web.archive.org/web/20160305002947/https://www.nasa.gov/feature/methane-snow-on-pluto-s-peaks/|archive-date=March 5, 2016 |last1=Talbert |first1=Tricia }}</ref>

== See also ==
'''Lexicon'''
* [[Eskimo words for snow]]
* [[The wrong type of snow]]
'''Notable snow events'''
* [[2007 Siberian orange snow]]
* [[Alberta clipper]]
* [[List of blizzards]]
* [[List of snowiest places in the United States by state]]
'''Recreation'''
* [[Skiing]]
* [[Sled]]
* [[Snow angel]]
* [[Snow cannon]]
* [[Snowman]]
* [[Snowmobiling]]
* [[Winter sport]]
'''Related concepts'''
* [[Blizzard]]
* [[Freezing rain]]
* [[Frost]]
* [[Graupel]]
* [[Hail]]
* [[Ice]]
* [[Ice pellets]]
* [[Hard rime|Rime]]
* [[Rain and snow mixed|Sleet]]
* [[Snowbelt]]
'''Science and scientists'''
* [[Snow hydrology]]
* [[Timeline of snowflake research]]
* [[Ukichiro Nakaya]]
'''Snow structures'''
* [[Igloo]]
* [[Quinzhee]]
* [[Snow cave]]
* [[Snow grooming]]

== References ==
{{Reflist|30em}}

== External links ==
{{Sister project links|Snow}}
* [http://www.unep.org/geo/geo%5Fice/ United Nations Environment Programme: Global Outlook for Ice and Snow] {{Webarchive|url=https://web.archive.org/web/20070608011925/http://www.unep.org/geo/geo_ice/ |date=June 8, 2007 }}
* [http://www.lowtem.hokudai.ac.jp/en/index.html Institute of Low Temperature Science, Hokkaido University]
* [https://www.wsl.ch/en/snow-and-ice.html Swiss Federal Institute for Forest, Snow and Landscape Research]
* [http://nsidc.org National Snow and Ice Data Center of the United States]
* [http://design.medeek.com/resources/snow/groundsnowloads.html American Society of Civil Engineers ground snow loads interactive map for the continental US]
{{Good article}}

{{Nature}}
{{Authority control}}

[[Category:Snow| ]]
[[Category:Articles containing video clips]]
[[Category:Forms of water]]
[[Category:Water ice]]
[[Category:Precipitation]]
[[Category:Weather hazards]]