Snow Glossary


A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Ablation
Snow ablation usually refers to snow removal by melting and evaporation. The main factor that controls the rate of ablation is air temperature. Subsidiary factors include humidity, wind speed, direct solar radiation and rainfall. The rate of ablation of a snow-field is also affected by factors such as depth and age of the snow, the topography of the underlying surface, size, slope and aspect.

Accretion
Accretion is the growth of precipitation particles by collision of ice crystals with supercooled liquid droplets that freeze on impact.

Avalanche
A snow mass that has a volume greater than 100 cubic metres and a minimum length of 50m, that slides rapidly downhill of a mountain.

Avalanche Size
Extent of the avalanche, classified by the length, volume and destructive potential.

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Blizzard
Definition of a blizzard can be found in the Tab 'What is a blizzard?'

Blowing Snow/Drifting Snow
Snow that is transported by wind to heights above 1.8m above the ground, causing a reduction in visibility. Blowing snow is reported as 'BLSN' in a METAR observation.

Breakable Crust
Hard layer at the top of the surface of the snow that breaks when stepped upon.

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Corn Snow
Is wet snow, which consists of large grains that have occurred from repeated melt-freeze processes.

Cornice
An overhanging mass of snow created by the wind, usually near a ridge of a mountain.

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Dendrite
Hexagonal ice crystals with complex and often fernlike branches. A more detailed definition can be found in Chapter 1 of the PhD thesis.

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Firn
Partially compacted granular snow that is in the intermediate stage between snow and glacial ice. It is formed due to pressure of the overlying snow by the processes of compaction, recrystallization and melting. A German word by nature, meaning 'old snow'.

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Graupel
Snowflakes that become rounded pellets due to riming. Typical sizes are 2-5mm in diameter. Graupel is sometimes mistaken for hail. A more detailed definition can be found in Chapter 1 of the PhD thesis.

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Heavy Snow
Large snowflakes that greatly reduce the visibility and falls at a rate exceeding 4cm per hour.

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Metamorphism
Changes in the structure and texture of snow grains which results from variations in air temperature, migration of liquid water, water vapour and pressure within the snow cover.

Moderate Snow
Large snowflakes that fall and greatly impair visibility. The snow cover increases in depth at a rate between 0.5cm to 4cm per hour.

Moist Snow
Snow that has no visible liquid water present. Moist snow is ideal snow for making snowballs etc.

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Polycrystal
A snowflake composed of many individual ice crystals.

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Sleet
Term also known as ice pellets in the U.S.A., when small bits of ice rebound from the surface after hitting the ground. Sleet (ice pellets) is reported as 'PE' in a METAR observation in the U.S.A, however it is reported as 'RASN' in an UK METAR observation, as sleet is regarded in the UK as snow and rain together.

Slight Snow
Snowflakes that are sparse and usually small. The rate of accumulation of the snow cover does not exceed 0.5cm per hour.

Slush
Snow or ice on the ground that has been altered by rain and/or temperatures higher than freezing point.

Snow
Frozen precipitation in the form of white or translucent ice crystals. These ice crystals are often complex in nature but portray a hexagonal format. Snow often falls from stratiform clouds, but can fall as snow showers from cumuliform clouds. Snow is reported as 'SN' in a METAR observation.

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Snow Banner
Snow that is blown off a peak of a mountain that visually shows a similarity of smoke escaping from a chimney.

Snow Blindness
Temporary blindness or impaired vision that has resulted from the sun's rays reflecting off a snow covered surface. The medical term for snow blindness is niphablepsia.

Snowboard
A solid, flat, white material, such as painted plywood, approximately 60cm on each side that is laid on the ground or on the surface of the snow by meteorological observers to obtain more accurate measurements of snowfall.

Snow Burn
Similar to sun burn a burn on the skin that has been caused by the sun's rays reflecting off a snow-covered surface.

Snow Bursts
Are very intense showers of snow, often of short duration, that greatly restrict visibility and produce periods of rapid snow accumulation.

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Snow Core
Is a sample of snow, either just from freshly fallen snow or combined old and new snow on the ground. This is obtained by pushing a cylinder down through the snow layer and extracting the snow.

Snow Cover
The extent of ground covered by snow that has been deposited by subsequent snowfalls. Snow cover is usually expressed as a percent of the total area of ground covered by snow.

Snow Creep
A continuous, extremely slow, downhill movements of a layer of snow down a mountainside.

Snow Crust
Fallen snow that has an icy surface due to the slight melting and re-freezing of the top layer.

Snow Day
In UK climatology, a snow day is where snow is observed to fall in a 24-hour period from midnight to midnight.

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Snow Density
The mass of snow per unit volume that is equal to the water content of snow divided by its depth.

Snow Depth/Snowfall
This is measured vertically with a graduated ruler and takes into account both old and new snow on the ground since the previous day, or, since the previous observation (expressed in cm). The snow depth measurement as rainfall (i.e. its water content) may be achieved in a suitable snow-gauge, or by melting the snow caught in a standard rain-gauge. The average annual number of days with snow falling on low ground up to approximately 70m above mean sea level increases in latitude and from west to east across the UK. This can range from less than 5 days in southern Cornwall to over 35 days in NE Scotland. At places 70m above mean sea level, the average number of days increases by approximately 1 day for every 15m of elevation. The average annual number of days with snow lying on the ground is one of the most variable of meteorological parameters over the UK. Environmental parameters which influence days with snow lying are monthly mean temperature, frequency of snowfall, quantity of snowfall and the character of the meteorological station and its surroundings. The average annual number of days with snow lying on the ground ranges from less than 5 days per year in southern and western coastal districts of SW England to over 100 days per year in Grampian.

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Snow Devil
This is generated by rotating winds that pick up 'loose' snow. This is formed by the convergence of local air currents. A snow devil may also be referred to, or known as a snowspout.

Snow Drift
This is wind-deposited snow. The result of drifting and blowing snow is usually a dense snow layer deposited on leeward slopes. Areas prone to deposition are adjacent to ridgelines, gullies and slope depressions or slope discontinuities.

Snow Eater
Any warm downslope wind that blows over and eventually melts any snow-covered ground.

Snowflake
An ice crystal or an aggregate of ice crystals in an infinite variety of shapes and forms that fall from clouds. More of a detailed definition can be found in Chapter 1 of the PhD.

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Snow Flurries/Snow Showers
Snow that falls for a short duration of time often light in intensity. Flurries usually produce little accumulation. Snow showers are reported as 'SHSN' in a METAR observation.

Snow Garland
Snow appearing as beautiful long thick ropes draped on trees, fences and other objects. Formed by the surface tension of thin films of water bonding individual snow crystals.

Snow-Gauge
A device for the retention and measurement of snow. In the Hellmann-Fuess snow-gauge the snow is caught in a receiver supported on a balance, the displacement of which is continuously recorded, so that an autographic record of snowfall is obtained. Most snow-gauges are, however, merely rain-gauges fitted with jackets or other devices to make them suitable for collecting solid precipitation and for melting it before taking the reading.

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Snow Grains
Frozen precipitation in the form of very small (less than 1mm), white opaque, flat or elongated grains of ice. Snow grains are viewed as the solid equivalent of drizzle. When the grains hit hard ground, they do not bounce or shatter. Snow grains are reported as 'SG' in a METAR observation.

Snow Level
The elevation in mountainous terrain where the precipitation changes from rain to snow, depending on the temperature structure of the associated air mass. The snowfall level is usually about 300m lower than the freezing level. During heavy precipitation the snowfall limit can be about 600m below the freezing level.

Snow Line
The lowest topographic limit of a permanent snow field. Depending on the slope of the mountain, the snow line can vary greatly in altitude.

Snow Load
The downward force on an object or structure caused by the weight of accumulated snow.

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Snow Thickness
The thickness of a snowpack measured to the perpendicular of the slope.

Snow water
Is the water content obtained from melting the snow.

Snow Lying
This definition is found within Chapter 2 of the PhD.

Snowpack
The total snow and ice on the ground, including both new snow and the previous snow and ice which has not melted.

Snow Pellets
Frozen precipitation (2-5mm in diameter) in the form of white, round or conical opaque grains of ice. The pellets are easily crushed and generally break up after rebounding from a hard surface, unlike hail. Sometimes snow pellets are called small or soft hail. Snow pellets are reported as 'GS' in a METAR observation.

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Snow Roller
The product of moist, cohesive snow that when initiated by wind rolls across the landscape, gathers snow until it can no longer move. It is shaped like a rolled sleeping bag, some reaching 1m across and 2m in diameter.

Snow Squall
Is a brief, but intense fall of snow that greatly reduces visibility and which is often accompanied by strong winds.

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Thaw
A warm spell of weather when ice and snow melts.

Thunder Snow
A wintertime thunderstorm from which snow falls instead of rain. Temperatures below freezing point within the atmosphere discourage the melting of snow into rain. Intense snowfall rates often occur during these situations.

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Wet Snow
Snow that has visible liquid water present and can be pressed out of a snow sample.

Whiteout
When visibility is near zero due to blizzard conditions or occurs on sunless days when clouds and surface snow seem to blend, erasing the horizon completely.

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Snowcast

Snow forecast for the period 18 - 24 December 2016 across the UK

18th - None

19th - None

20th - None

21st - None

22nd - Western and central Scotland

23rd - Western and central Scotland

24th - Western and central Scotland