Any skier or snowboarder knows that snow does not come in just one form. Snowpacks are as variable as the snowflakes that form them. We have all heard the claim that Eskimos have dozens of words for snow (actually, I discovered, just more flexibility in how root words are modified), but what about our terms for snow? Skiers talk about corduroy and corn snow, but the variation in snow types extends beyond the ski slopes.
Snow forms when the atmospheric temperature is at or below freezing. In certain conditions, it is even possible for snow to reach the ground when the ground temperature is 41 degrees Fahrenheit. Freezing atmospheric temperatures, combined with moisture in the air, forms snow crystals. Snow crystals exist in four forms: snowflakes, hoarfrost, graupel, and polycrystals.
- Snowflakes, which we are all familiar with, are clusters of ice crystals that fall from clouds. Their shape is dependent on the conditions in which they are formed and through which they fall.
- Hoarfrost is our name for ice crystals that form on small surfaces that are open to the air. When a surface’s temperature is lower than the frost point of the surrounding air, moisture transforms directly from vapor to solid, forming delicate laces of surficial ice.
- Graupel is the round, pellet-like snow that resembles a softer hail. When ice crystals fall through super-cooled cloud droplets (which remain liquid although they are below freezing temperatures), the droplets freeze to the crystals, forming a clump.
- Polycrystals are flakes made up of many individual crystals.
The National Snow and Ice Data Center has gone one step further and categorized the types of snow cover, or snowpack. Snowpack is defined as all the snow and ice that lies on the ground at a given time, including fresh snow and any older snow still on the ground. Its composition is affected by air and ground temperatures, temperature stability, wind, and the length of time that snow stays on the ground. The six types of snowpack are: new snow, firn, névé, old snow, perennial snow, and powder snow.
- New snow is snow that accumulated recently enough that the original form of its ice crystals is still recognizable, as when snowflakes’ delicate shapes are still visible on top of a layer of fresh pow.
- Firn is snowpack older than one year. It is dense and well-bonded.
- Névé is young, granular snow that has been partially melted and then refrozen. This process hardens and compacts it. If névé lasts longer than a year, it becomes firn. This is the main snowpack type resulting in glacier formation.
- Old snow has been transformed enough that its ice crystals’ original form is not recognizable. The amount of time new snow takes to become old snow depends on a number of factors.
- Perennial snow, as its name suggests, is snowpack that never melts but stays on the ground year after year.
- Powder snow is fresh, dry snow comprised of loose crystals.
Consider this the next time a friend invites you to hit the slopes. Is it really powder you’re carving or is it old snow?
Don’t even get me started on the different types of snowfall (blizzard, snowstorm, snow flurry, snow squall, snowburst, blowing snow, drifting snow).