Snow is defined as ‘the aqueous vapour of the atmosphere precipitated in partially frozen crystalline form and falling to the earth in white flakes’. (Macquarie Dictionary 1998).
When the temperature falls to below freezing, drops of water are deposited on dust particles in the air and snowflakes form. Their size and shape depend on the amount of moisture in the air and on the temperature, but each snow crystal is hexagonal with unique features, The hardness and sharpness of these crystals determines snow properties. The lower the temperature, the drier and harder the snow crystals.
While falling, the snowflakes are worn down and rounded by the wind. When they reach the ground, a change process starts. As fallen snow gets older, it settles, further rounding off the crystals. The crystals are broken down into fine grains at a rate that increases with the temperature. At temperatures above freezing, the crystals start to melt. The higher the temperature, the wetter and softer the snow crystals, and the lower the temperature, the harder and drier the crystals. After a few days, the crystals have usually disappeared and been replaced by coarse grains or ‘corn’ snow.
Snow can be categorised according to its age and the effects of weather. Newly fallen snow looks like the traditional six-sided crystals. In Australia, this type of snow frequently falls in large ‘clumps’, and remains on the ground in that form for some time. Freshly fallen snow maintains its crystal structure for a long time, providing the temperature remains below freezing and the snow crystal structure is not broken by the wind. Most newly fallen snow is ideal for skiing on, since there is a good deal of air mixed in with the mass. The snow will compact easily and provide a smooth base for skiing. Newly fallen snow that is mostly air is known as ‘powder snow’ and is not all that common in Australia.