| Section S | S index | 551-559 of 1376 terms |
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snow crust—A crisp, firm, outer surface upon snow. Basically, three types of snow crusts exist, formed by 1) the refreezing of surface snow, after melting and/or wetting, to form a hard layer of snow (sun crust, rain crust, spring crust); 2) the packing of snow into a hard layer by wind action (wind crust, wind slab); and 3) the freezing of surface water, however derived, to form a continuous layer of ice on top of snow (film crust, ice crust). A snow crust is designated as “breakable” or “unbreakable” according to its ability to support a person on skis.
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snow crystal—Any of several types of ice crystal found in snow. A snow crystal is a single crystal, in contrast to a snowflake, which is usually an aggregate of many single snow crystals.
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snow day—A day on which a fall of snow is observed.
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snow density—The ratio of the volume of meltwater that can be derived from a sample of snow to the original volume of the sample; strictly speaking, this is the specific gravity of the snow sample. Freshly fallen snow usually has a snow density of 0.07 to 0.15; glacial ice formed from compacted snow (or firn) has a maximum density of about 0.91. Values as low as 0.004 have been measured. Compare water content, water equivalent.
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snow eater—1. Any warm wind blowing over a snow surface; usually applied to a foehn wind, that is, schneefresser. See also chinook. 2. A fog over a snow surface; so called because of the frequently observed rapidity with which a snow cover disappears after a fog sets in. As water vapor from the air condenses on the snow, the latent heat of condensation causes the snow to become warmer and melt faster.
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snow fence—1. An open, slatted board fence usually 1–3 m high, placed upwind of a railroad track or highway. The fence serves to create eddies in the downstream airflow, resulting in a reduced wind speed such that snow is deposited close to the fence on its leeward side. The intent is to provide a comparatively clear zone along the railroad track or highway. A snow fence is also used to accumulate drifting snow in a flat windswept area to reduce the depth of ground frost and increase soil moisture as the snow melts. 2. Same as Wild fence.
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snow flurry—Common term for a light snow shower, lasting for only a short period of time.
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snow forest climate—A major category (the D climates) in W. Köppen's climatic classification, defined by a coldest-month mean temperature of less than −3°C (26.6°F) and a warmest-month mean temperature of greater than 10°C (50°F). The first limit separates it from temperate rainy climates, and the second from tundra climates. It is distinguished from the dry climates by a function of annual temperature and precipitation (see formulas under steppe climate). The outstanding feature of these climates is the cold winters with at least a month of snow-covered ground. These are the coldest of the tree climates. In C. W. Thornthwaite's classifications, this general type of climate would be 1) in the 1931 system, humid or subhumid and microthermal climate, or taiga climate; and 2) in the 1948 system, humid or moist subhumid and microthermal climate.
Köppen, W. P., and R. Geiger, 1930–1939: Handbuch der Klimatologie, Berlin: Gebruder Borntraeger, 6 vols
Thornthwaite, C. W., 1931: The climates of North America according to a new classification. Geogr. Rev., 21, 633–655.
Thornthwaite, C. W., 1948: An approach toward a rational classification of climate. Geogr. Rev., 38, 55–94.
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snow garland—A rare and beautiful phenomenon in which snow is festooned from trees, fences, etc., in the form of a rope of snow, several feet long and several inches in diameter, formed and sustained by surface tension acting in thin films of water bonding individual crystals. Such garlands form only when the surface temperature is close to the melting point, for only then will the requisite films of slightly supercooled water exist.
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