Idea to combine the three different classification article sections from

Proposed consolidation[edit]

An early classification of snowflakes by Israel Perkins Warren.^[1]

Snowflakes form in a wide variety of intricate shapes. Although nearly-identical snowflakes have been made in a laboratory, they are unlikely to be found in nature.^[2]^[3]^[4]^[5] Initial attempts to find identical snowflakes by photographing thousands of them with a microscope from 1885 onward by Wilson Alwyn Bentley found the wide variety of snowflakes that are known about today.

Ukichiro Nakaya developed a crystal morphology diagram, relating crystal shape to the temperature and moisture conditions under which they formed^[6]^[7] . Nakaya also discovered that shape is additionally influenced by whether the vapour pressure is above or below saturation. Below saturation, crystals trend more towards solid and compact. Under supersaturated conditions, shapes trend towards lacy, delicate, and ornate.

A summary of his findings is shown in the table below.

Crystal structure morphology as a function of temperature, water saturation, and saturation conditions.
Temperature range		Saturation range		Snow crystal type
°C	°F	g/m³	oz/cu yd	below saturation	above saturation
0 to −3.5	32 to 26	0.0 to 0.5	0.000 to 0.013	Solid Plates	Thin Plates Dendrites
−3.5 to −10	26 to 14	0.5 to 1.2	0.013 to 0.032	Solid Prisms Hollow Columns	Hollow Columns Needles
−10 to −22	14 to −8	1.2 to 1.4	0.032 to 0.038	Thin Plates Solid Plates	Sectored Plates Dendrites
−22 to −40	−8 to −40	1.2 to 0.1	0.0324 to 0.0027	Plates	Columns

Depending on the atmospheric conditions and ice nuclei, more complex growth patterns also form side-planes, bullet-rosettes, and planar types.^[8]^[9]^[10] For instance, if a crystal started forming in a column growth regime (at around −5 °C/23 °F) 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".^[7]

Magono and Lee devised a classification of freshly formed snow crystals that includes 80 distinct shapes^[11]. The main categories are:

Crystal Category	Symobol	Subdivision
Needle	N	Simple needles Combination of needles
Columnar	C	Simple columns Combination of colums
Plate	P	Regular crystal in one plane Plane crystal with extensions Crystal with irregular number of branches Crystal with 12 branches Malformed crystal Radiating assemblage of plane branches
Columnar and plate combination	CP	Column with plane crystal at both ends Bullet with plane crystals Plane crystal with spatial extensions at ends
Side planes	S	Side planes Scalelike side planes Combination of side planes, bullets, and columns
Rimed	R	Rimed crystal Densely rimed crystal Graupellike crystal Graupel
Irregular	I	Ice particle Rimed particle Broken piece from a crystal Miscellaneous
Germ	G	Minute column Germ of skeleton form Minute hexagonal plate Minute stellar crystal Minute assemblage of plates Irregular germ

The International Classification for Seasonal Snow on the Ground describes snow crystal classification, once deposited on the ground, including grain shape and grain size. The system also characterizes the snowpack, as the individual crystals metamorphize and coalesce.^[12]

^ Warren, Israel Perkins (1863). Snowflakes: a chapter from the book of nature. Boston: American Tract Society. p. 164. Retrieved 2016-11-25.
^ Kenneth G. Libbrecht. "Identical-Twin Snowflakes".
^ Cite error: The named reference John Roach was invoked but never defined (see the help page).
^ Jon Nelson (2008-09-26). "Origin of diversity in falling snow" (PDF). Atmospheric Chemistry and Physics. 8 (18): 5669–5682. Bibcode:2008ACP.....8.5669N. doi:10.5194/acp-8-5669-2008. Archived (PDF) from the original on 2011-11-20. Retrieved 2011-08-30.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ Libbrecht, Kenneth (Winter 2004–2005). "Snowflake Science" (PDF). American Educator. Archived from the original (PDF) on 2008-11-28. Retrieved 2009-07-14.
^ Bishop, Michael P.; Björnsson, Helgi; Haeberli, Wilfried; Oerlemans, Johannes; Shroder, John F.; Tranter, Martyn (2011). Singh, Vijay P.; Singh, Pratap; Haritashya, Umesh K. (eds.). Encyclopedia of Snow, Ice and Glaciers. Springer Science & Business Media. p. 1253. ISBN 978-90-481-2641-5.
^ ^a ^b Cite error: The named reference natgeojan07 was invoked but never defined (see the help page).
^ Matthew Bailey; John Hallett (2004). "Growth rates and habits of ice crystals between −20 and −70C". Journal of the Atmospheric Sciences. 61 (5): 514–544. Bibcode:2004JAtS...61..514B. doi:10.1175/1520-0469(2004)061<0514:GRAHOI>2.0.CO;2.
^ Kenneth G. Libbrecht (2006-10-23). "A Snowflake Primer". California Institute of Technology. Archived from the original on 2009-07-10. Retrieved 2009-06-28.
^ Kenneth G. Libbrecht (January–February 2007). "The Formation of Snow Crystals". American Scientist. 95 (1): 52–59. doi:10.1511/2007.63.52.
^ Magono, Choji; Lee, Chung Woo (1966). "Meteorological Classification of Natural Snow Crystals". Journal of the Faculty of Science. 7. 3 (4) (Geophysics ed.). Hokkaido: 321–335. hdl:2115/8672.
^ Fierz, C.; Armstrong, R.L.; Durand, Y.; Etchevers, P.; Greene, E.; et al. (2009), The International Classification for Seasonal Snow on the Ground (PDF), IHP-VII Technical Documents in Hydrology, vol. 83, Paris: UNESCO, p. 80, archived (PDF) from the original on 2016-09-29, retrieved 2016-11-25

[1] Warren, Israel Perkins (1863). Snowflakes: a chapter from the book of nature. Boston: American Tract Society. p. 164. Retrieved 2016-11-25.

[2] Kenneth G. Libbrecht. "Identical-Twin Snowflakes".

[John_Roach-3] Cite error: The named reference John Roach was invoked but never defined (see the help page).

[4] Jon Nelson (2008-09-26). "Origin of diversity in falling snow" (PDF). Atmospheric Chemistry and Physics. 8 (18): 5669–5682. Bibcode:2008ACP.....8.5669N. doi:10.5194/acp-8-5669-2008. Archived (PDF) from the original on 2011-11-20. Retrieved 2011-08-30.{{cite journal}}: CS1 maint: unflagged free DOI (link)

[5] Libbrecht, Kenneth (Winter 2004–2005). "Snowflake Science" (PDF). American Educator. Archived from the original (PDF) on 2008-11-28. Retrieved 2009-07-14.

[Snowenclyclopedia-6] Bishop, Michael P.; Björnsson, Helgi; Haeberli, Wilfried; Oerlemans, Johannes; Shroder, John F.; Tranter, Martyn (2011). Singh, Vijay P.; Singh, Pratap; Haritashya, Umesh K. (eds.). Encyclopedia of Snow, Ice and Glaciers. Springer Science & Business Media. p. 1253. ISBN 978-90-481-2641-5.

[natgeojan07-7] Cite error: The named reference natgeojan07 was invoked but never defined (see the help page).

[BaileyHallett-8] Matthew Bailey; John Hallett (2004). "Growth rates and habits of ice crystals between −20 and −70C". Journal of the Atmospheric Sciences. 61 (5): 514–544. Bibcode:2004JAtS...61..514B. doi:10.1175/1520-0469(2004)061<0514:GRAHOI>2.0.CO;2.

[9] Kenneth G. Libbrecht (2006-10-23). "A Snowflake Primer". California Institute of Technology. Archived from the original on 2009-07-10. Retrieved 2009-06-28.

[10] Kenneth G. Libbrecht (January–February 2007). "The Formation of Snow Crystals". American Scientist. 95 (1): 52–59. doi:10.1511/2007.63.52.

[magono-lee-11] Magono, Choji; Lee, Chung Woo (1966). "Meteorological Classification of Natural Snow Crystals". Journal of the Faculty of Science. 7. 3 (4) (Geophysics ed.). Hokkaido: 321–335. hdl:2115/8672.

[Classificationonground-12] Fierz, C.; Armstrong, R.L.; Durand, Y.; Etchevers, P.; Greene, E.; et al. (2009), The International Classification for Seasonal Snow on the Ground (PDF), IHP-VII Technical Documents in Hydrology, vol. 83, Paris: UNESCO, p. 80, archived (PDF) from the original on 2016-09-29, retrieved 2016-11-25

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