The type of precipitation formed when water vapour condenses at a temperature below freezing point, so passing directly from the gaseous to the solid stage, and forming minute spicules of ice. These unite into crystals which are either ‘flat hexagonal plates’ or ‘hexagonal prisms’, revealing infinite variations in their patterns. These crystals aggregate into Snow Flakes, where the lower atmosphere is sufficiently cool, they will reach the ground without melting. Snow may be dry and powdery under low temperature conditions, as in Antarctica.
Snow Avalanche- A fall of snow down a hill side is called Snow Avalanche. It may be-
1. Wind Slab- where the snow is crusted and compacted.
2. A dry Snow Avalanche- usually of new snow in winter and
3. A Wet Snow Avalanche- caused by a sudden spring thaw.
Snow Drift- A bank of snow drifted by the wind which has accumulated against obstacles, sometimes to great depths; this may block roads and railway lines, unless protected by barriers, sheds or snow drift fences.
Snow Field- An area of permanent snow which has accumulated in a basin shaped hollow among the mountains or on a plateau; for example, the Ewig Schneefeld near the Jungrau in the Bernese Oberland.
Snow Line- The lowest edge of a more or less continuous snow cover is called a snow line.
The Permanent Snow Line- is the level at which wastage of snow by melting in summer fails to remove winter accumulation. This varies with latitude, altitude and aspect. At the poles it lies at sea level, in south Greenland at 2000 feet, in Norway at 4 to 5000 feet, in the Alps about 9000 feet, in Eastern Africa at 16000 feet.
The Winter Snow Line-fluctuates from year to year, but is markedly lower than the permanent snowline. There is no permanent snow line in Great Britain, though in winter in the Highlands of Scotland snowline lies above 3000 feet for about 80 days.