Classification of snow on the ground comes from two sources: the science community and the community of those who encounter it in their daily lives. Snow on the ground exists both as a material with varying properties and as a variety of structures, shaped by wind, sun, temperature, and precipitation. on the snow surface from crystallized water vapor emerging on a cold, clear night .
Classification of snowpack material properties The
International Classification for Seasonal Snow on the Ground describes snow crystal classification, once it is deposited on the ground, that include grain shape and grain size. The system also characterizes the snowpack, as the individual crystals metamorphize and coalesce. It uses the following characteristics (with units) to describe deposited snow: microstructure, grain shape, grain size (mm), snow density (kg/m3), snow hardness, liquid water content, snow temperature (°C), impurities (mass fraction), and layer thickness (cm). The grain shape is further characterized, using the following categories (with code): precipitation particles (PP), machine-made snow (MM), decomposing and fragmented precipitation particles (DF), rounded grains (RG), faceted crystals (FC), depth hoar (DH), surface hoar (SH), melt forms (MF), and ice formations (IF). Other measurements and characteristics are used as well, including a snow profile of a vertical section of the snowpack. Snow travelers consider the thickness and resulting strength of a crust to determine whether it is "unbreakable", meaning that they will support the weight of the traveler or "breakable", meaning that it will not. •
Depth hoar –
Depth hoar comprises faceted snow crystals, usually poorly or completely unbonded (unsintered) to adjacent crystals, creating a weak zone in the snowpack. Depth hoar forms from metamorphism of the snowpack in response to a large temperature gradient between the warmer ground beneath the snowpack and the surface. The relatively high porosity (percentage of air space), relatively warm temperature (usually near freezing point), and unbonded weak snow in this layer can allow various organisms to live in it.
Wind-induced •
Cornice – Wind blowing over a ridge can create a compacted
snowdrift with an overhanging top, called a
cornice. Cornices present a hazard to mountaineers, because they are prone to break off. •
Pillow drift – A pillow drift is a snow drift crossing a roadway and usually 3 to 4.5 metres (10–15 feet) in width and 30 cm to 90 cm (1–3 feet) in depth. •
Sastrugi –
Sastrugi are snow surface features sculpted by wind into ridges and grooves up to 3 meters high, with the ridges facing into the prevailing wind. •
Snowdrift –
Snowdrifts are wind-driven accumulations of snow deposited downwind of obstructions. •
Wind crust – A layer of relatively stiff, hard snow formed by deposition of wind blown snow on the windward side of a ridge or other sheltered area. Wind crusts generally bond better to snowpack layers below and above them than wind slabs. •
Wind slab – A layer of relatively stiff, hard snow formed by deposition of wind blown snow on the leeward side of a ridge or other sheltered area. Wind slabs can form over weaker, softer freshly fallen powder snow, creating an avalanche hazard on steep slopes. •
Névé –
Névé is a young, granular type of
snow which has been partially melted, refrozen and compacted, yet precedes the form of ice. This type of snow is associated with
glacier formation through the process of
nivation. Névé that survives a full season of
ablation turns into
firn, which is both older and slightly denser. •
Suncups –
Suncups are polygonal depressions in a
snow surface that form patterns with sharp narrow ridges separating smoothly concave quasi-periodic hollows. They form during the
ablation (melting away) of snow from
incident solar radiation in bright
sunny conditions, sometimes enhanced by the insulating presence of dirt along the ridges. •
Yukimarimo –
Yukimarimo are balls of fine
frost, formed at low temperatures on the
Antarctic Plateau during light or calm winds.
Ski resort classification Ski resorts use standardized terminology to describe their snow conditions. In North America terms include: •
Base snow – Snow that has been thoroughly consolidated. •
Frozen granular – Snow whose granules have frozen together. •
Loose granular – Snow with incohesive granules. •
Machine-made – Produced by snow cannons, and typically denser than natural snow. •
New snow – Snow that has fallen since the previous day's report. •
Packed powder – Powder snow that has been compressed by
grooming or by ski traffic. •
Powder – Freshly fallen, uncompacted snow. The density and moisture content of powder snow can vary widely; snowfall in coastal regions and areas with higher humidity is usually heavier than a similar depth of snowfall in an arid or continental region. Light, dry (low moisture content, typically 4–7% water content) powder snow is prized by skiers and snowboarders. •
Packing snow – Packing snow is at or near the melting point, so that it can easily be packed into snowballs and thrown or used in the construction of a snowman, or a
snow fort. •
Slush –
Slush is substantially melted snow with visible water in it. •
Snirt – Snirt is an informal term for snow covered with dirt, especially where strong winds pick up topsoil from uncovered farm fields and blow it into nearby snowy areas. Also, dirty snow left over from plowing operations. •
Spring snow – Spring snow describes a variety of temperature and moisture conditions with corn snow. ==In various cultures==