AskDefine | Define snowfall

Dictionary Definition

snowfall n : precipitation falling from clouds in the form of ice crystals [syn: snow]

User Contributed Dictionary

English

Alternative forms

Noun

  1. An instance of falling of snow.
    There has been a snowfall every day this week.
  2. The amount of snow that falls on one occasion.
    London recorded a snowfall of 10 centimetres last night.

Translations

instance of falling of snow
  • Finnish: lumisade
  • German: Schneefall
  • Hungarian: hóesés
  • Italian: nevicata
amount of snow that falls on one occasion
  • Italian: nevicata

Extensive Definition

Snow is a type of precipitation in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. The process of precipitation is called snowfall.
Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by external pressure. The METAR code for snow is SN.

Snowflakes

Snow forms when water vapor condenses directly into ice crystals, usually in a cloud. Floating cloud particles (ice nucleators, often of biological origin ) are needed in order for snowflakes to form at temperatures above -40C. 85% of these nuclei are airborne bacteria, with dust particles making up the rest. The ice crystals which form around the ice nucleators typically have a diameter of several milimetres and usually have six lines of symmetry. A snowflake is an aggregate of such ice crystals and may be several centimeters large. The term "snowflake" is also used below for the symmetrical ice crystals themselves. The individual ice crystals are clear but because of the amount of light the individual crystals reflect snowflakes appear white in color unless contaminated by impurities.

Geometry

Large, well formed snowflakes are relatively flat and have six approximately identical arms, so that the snowflake nearly has the same 6-fold dihedral symmetry as a regular hexagon or hexagram. This symmetry arises from the hexagonal crystal structure of ordinary ice. However, the exact shape of the snowflake is determined by the temperature and humidity at which it forms. Snowflakes are not perfectly symmetrical however. The most common snowflakes are visibly irregular, although near-perfect snowflakes may be more common in pictures because they are more visually appealing.
Snowflakes can come in many different forms, including columns, needles, bricks and plates (with and without "dendrites" - the "arms" of some snowflakes). These different forms arise out of different temperatures and water saturation - among other conditions. Six petaled ice flowers grow in air between and . The vapor droplets solidify around a dust particle. Between temperatures of and , the snowflake will be in the form of a dendrite or a plate or the six petaled ice flower. As temperatures get colder, between and , the crystals will form in needles or hollow columns or prisms. When the temperature becomes even colder from to the ice flowers are formed again, and at temperatures below , the vapors will turn into prisms again. If a crystal has started forming at around , and is then exposed to warmer or colder temperatures, a capped column may be formed which consists of a column-like design capped with a dendrite or plate-like design on each end of the column.
Spring snow melt is a major source of water supply to areas in temperate zones near mountains that catch and hold winter snow, especially those with a prolonged dry summer. In such places, water equivalent is of great interest to water managers wishing to predict spring runoff and the water supply of cities downstream. Measurements are made manually at marked locations known as snow courses, and remotely using special scales called snow pillows.
Many rivers originating in mountainous or high-latitude regions have a significant portion of their flow from snowmelt. This often makes the river's flow highly seasonal resulting in periodic flooding. In contrast, if much of the melt is from glaciated or nearly glaciated areas, the melt continues through the warm season, mitigating that effect.

Energy balance

The energy balance of the snowpack is dictated by several heat exchange processes. The snowpack absorbs solar shortwave radiation that is partially blocked by cloud cover and reflected by snow surface. A longwave heat exchange takes place between the snowpack and its surrounding environment that includes overlaying air mass, tree cover and clouds. Convective (sensible) heat exchange between the snowpack and the overlaying air mass is governed by the temperature gradient and wind speed. Moisture exchange between the snowpack and the overlaying air mass is accompanied with latent heat transfer that is influenced by vapor pressure gradient and air wind. Rain on snow could induce significant heat input to the snowpack. A generally insignificant conductive heat exchange takes place between the snowpack and the underlying ground. That is the reason there is a small temperature rise after or before the snowfall.

Effects on human society

Activity

Substantial snowfall can disrupt public infrastructure and services, slowing human activity even in regions that are accustomed to such weather. Air and ground transport may be greatly inhibited or shut down entirely. Populations living in snow-prone areas have developed various ways to travel across the snow, such as skis, snowshoes, and sleds pulled by horses, dogs, or other animals. Basic infrastructures such as electricity, telephone lines, and gas supply can also fail. In addition, snow can make roads much harder to travel and cars attempting to traverse them can easily become stuck. The combined effects can lead to a "snow day" on which gatherings such as school, work, or church are officially canceled. In areas that normally have very little or no snow, a snow day may occur when there is only light accumulation or even the threat of snowfall, since those areas are ill-prepared to handle any amount of snow.

Agriculture

Snowfall can be beneficial to agriculture by serving as a thermal insulator, conserving the heat of the Earth and protecting 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.

Conservation

In areas near mountains, people have harvested snow and stored it as layers of ice covered by straw or sawdust in icehouses. This allowed the ice to be used in summer for refrigeration or medical uses.

Damage

A mudslide, flash flood, or avalanche can occur when excessive snow has accumulated on a mountain and there is a sudden change of temperature. Large amounts of snow that accumulate on top of man-made structures can lead to structural failure.

Records

The highest seasonal total snowfall ever measured was at Mount Baker Ski Area, outside of the town Bellingham, Washington in the United States during the 19981999 season. Mount Baker received 1,140 inches (29 m) of snow, thus surpassing the previous record holder, Mount Rainier, Washington, which during the 19711972 season received 1,122 in. (28.5 m) of snow. Guinness World Records list the world’s largest snowflakes as those of January 1887 at Fort Keogh, Montana;. allegedly one measured 15 inches (38 cm) wide.

Recreation

Types of snow

Falling snow

: A long-lasting snow storm with intense snowfall and usually high winds. Particularly severe storms can create whiteout conditions where visibility is reduced to less than 1 m.:A class of snow flakes that is shaped like a six sided column. One of the 4 classes of snow flakes.:A class of snow flakes that has 6 points, making it somewhat star shaped. The classic snow flake shape. One of the 4 classes of snow flakes.: A period of light snow with usually little accumulation with occasional moderate snowfall.: Supercooled rain that freezes on impact with a sufficiently cold surface. This can cover trees in a uniform layer of very clear, shiny ice – a beautiful phenomenon, though excessive accumulation can break tree limbs and utility lines, causing utility failures and possible property damage.

References

External links

snowfall in Afrikaans: Sneeu
snowfall in Arabic: ثلج
snowfall in Aragonese: Nieu
snowfall in Asturian: Ñeve
snowfall in Aymara: Khunu
snowfall in Azerbaijani: Qar
snowfall in Min Nan: Seh
snowfall in Belarusian (Tarashkevitsa): Сьнег
snowfall in Bosnian: Snijeg
snowfall in Bulgarian: Сняг
snowfall in Catalan: Neu
snowfall in Chuvash: Юр
snowfall in Czech: Sníh
snowfall in Welsh: Eira
snowfall in Danish: Sne
snowfall in Pennsylvania German: Schnee
snowfall in German: Schnee
snowfall in Navajo: Yas
snowfall in Estonian: Lumi
snowfall in Modern Greek (1453-): Χιόνι
snowfall in Emiliano-Romagnolo: Naiv
snowfall in Spanish: Nieve
snowfall in Esperanto: Neĝo
snowfall in Basque: Elur
snowfall in Persian: برف
snowfall in French: Neige
snowfall in Western Frisian: Snie
snowfall in Galician: Neve
snowfall in Korean: 눈 (날씨)
snowfall in Hindi: हिमपात
snowfall in Croatian: Snijeg
snowfall in Ido: Nivo
snowfall in Indonesian: Salju
snowfall in Icelandic: Snjór
snowfall in Italian: Neve
snowfall in Hebrew: שלג
snowfall in Georgian: თოვლი
snowfall in Swahili (macrolanguage): Theluji
snowfall in Kurdish: Berf
snowfall in Latin: Nix
snowfall in Latvian: Sniegs
snowfall in Lithuanian: Sniegas
snowfall in Lingala: Neje
snowfall in Hungarian: Hó
snowfall in Malay (macrolanguage): Salji
snowfall in Mongolian: Цас
snowfall in Dutch: Sneeuw
snowfall in Dutch Low Saxon: Snee
snowfall in Japanese: 雪
snowfall in Norwegian: Snø
snowfall in Norwegian Nynorsk: Snø
snowfall in Occitan (post 1500): Nèu
snowfall in Piemontese: Fiòca
snowfall in Polish: Śnieg
snowfall in Portuguese: Neve
snowfall in Romanian: Zăpadă
snowfall in Quechua: Rit'i
snowfall in Russian: Снег
snowfall in Scots: Snaw
snowfall in Albanian: Dëbora
snowfall in Simple English: Snow
snowfall in Slovak: Sneh
snowfall in Slovenian: Sneg
snowfall in Serbian: Снијег
snowfall in Sundanese: Salju
snowfall in Finnish: Lumi
snowfall in Swedish: Snö
snowfall in Tamil: பனித்தூவி
snowfall in Thai: หิมะ
snowfall in Vietnamese: Tuyết
snowfall in Cherokee: ᎤᎾᏥ
snowfall in Turkish: Kar
snowfall in Ukrainian: Сніг
snowfall in Yiddish: שניי
snowfall in Contenese: 雪
snowfall in Samogitian: Snėigs
snowfall in Chinese: 雪

Synonyms, Antonyms and Related Words

avalanche, blizzard, crystal, driven snow, flake, flurry, granular snow, igloo, mantle of snow, mogul, slosh, slush, snow, snow banner, snow bed, snow blanket, snow blast, snow fence, snow flurry, snow roller, snow slush, snow squall, snow wreath, snow-crystal, snowball, snowbank, snowbridge, snowcap, snowdrift, snowfield, snowflake, snowland, snowman, snowscape, snowshed, snowslide, snowslip, snowstorm, wet snow
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