MASTERCLASS
There’s more to winter’s meteorological phenomena than meets the eye, so it’s worth learning how to navigate, or avoid, the white stuff in its many forms.
■ SNOW IN THE AIR
It’s the snow that makes all other snow. But what actually is it? Snow forms around tiny ice particles which are formed in one of two ways. Either it is extremely blummin’ cold xxxxxxx xxxxxxxxxxxxx (-35°C or lower) causing vapour droplets to freeze together on contact and make an ice particle. Or ice forms around other microscopic particles like pollen or dust.
Some ice particles stick to others as they fall to the ground, joining in a hexagonal structure – a snowflake. If it’s very cold and the air is very humid, this falls to the ground as a dendrite, the most typical snowflake form. But if it's warmer than 0°C, snowflakes melt around the edges and clump together.
This is most of what we get in the UK.
■ FIRN
Snow that has made it through at least one summer and is now in the intermediate stage between snow and glacial ice. Firn is granular and partially compacted, a bit like wet sugar in appearance but much more dense in texture.
■ GRAUPEL
Graupel or ‘soft hail’ looks like tiny white ball bearings which can roll or blow away easily when disturbed. It’s actually a combination of snow and ice, which forms when rime ice forms a crust around a snowflake. This usually happens in turbulent weather, when snowflakes fall and are then blown upwards again into extremely cold levels of the atmosphere. Graupel is very noticeable on the surface but can also lie in layers under the snowpack, creating considerable avalanche risk.
■ HAIL
Hailstones are balls of solid ice – as you’ll know if one has ever hit you in the face. They form in thunderclouds when water droplets are swept up and down in the air. When they are swept to the top of a cloud in an updraft, they freeze, collecting ice until they become so heavy that they fall through the updraft and plummet to earth. Because they are so large, they don’t have time to melt before they hit the ground.
■ HOAR FROST
Hoar frost is basically frozen dew. When it forms on the snow’s surface, or on any surface which is already sub-zero, it takes a brittle, feathery form. This can be a weakness in the snowpack if more snow falls on it.
■ NÉVÉ
The best type of snow for walking on: firm and stable with a satisfying crunch when you punch through the upper layer. It is snow which has partially melted and then refrozen, forming a compacted, well-bonded layer.
■ POWDER
Very loose, light snow which falls in sub-zero conditions and light wind. It is poorly bonded so very bad for snowballs and gruelling work to wade through. A dream for skiers though.
■ CORNICE
A cornice is made
