Alpine Skiing - Snow and Weather

Snow and Weather

Skiers and snowboarders can encounter a wide range of snow and weather conditions, in part due to the location of specific resorts and global weather patterns at the time. Natural snow ranges in consistency from light and powdery to dense and heavy, depending upon atmospheric conditions. Snow is often measured by moisture content. Some areas of the United States' Rocky Mountains, for example, can receive considerable amounts of snow with moisture content as low as three to five percent; in the Northeastern United States and the Alps, moisture content is more typically 15 percent or more. Snow made by mechanical snowmaking often has moisture content of 35 percent or more.

Temperatures play a critical role in snow moisture content, but other atmospheric conditions are also relevant. Air currents and other factors determine snow crystal shape; obviously, the farther apart given snow crystals are, the more air is contained in the newly settled snow, resulting in lower net moisture content in a given volume of snow. Snow produced mechanically typically has high relative moisture content and low amounts of loft because the crystal structure resembles small, dense pellets. Even the fluffiest snow has mass, and snow typically settles under its own weight after time. This is one reason why untouched snow measuring 20 cm on the day it falls might be measured at 15 cm the day following. Snow is also subject to sublimation — a process by which water can go directly from a frozen state to a gaseous state without first melting. It is this same process that ultimately makes ice cubes shrink in a freezer. There are other factors that impact snow beyond its moisture content and crystal shape, however. Snow is impacted by wind, sunlight, skier traffic, ambient air temperature, relative humidity and grooming equipment; all of these factors combine to change snow crystal shape and density over time.

Some of the common conditions include:

Powder

Light, fluffy snow, found during and immediately after snowfall. Skiing and snowboarding in deep powder snow is a favorite among skilled, experienced skiers and snowboarders; sometimes known as "powderhounds" hunting for the next big dump. Because Western snow generally has a lower moisture content, western powder is lighter and easier to ski than heavier eastern powder. Utah and Colorado snow is especially known for being extremely light and dry as well as a lot of snow found in New Zealand.

Packed Powder

Packed powder is compressed powder that is formed after the snow is groomed. Whereas hard pack (see below) is extremely dense and hard to ski on, packed powder is slightly less dense and able to support skis without sinking. This makes it very easy and fun to ski on.

Chowder

Chopped up powder. Powder that has fallen in the prior few days and remains light and fluffy but has been skied or tracked up.

Crud

Once powder snow settles and becomes tracked up by skiers and snowboarders it firms or freezes into texture that is challenging and usually undesirable. Crud may contain "chicken heads", balls of frozen snow.

Groomed or corduroy

Snow that has been tilled by a grooming machine. This snow condition is favored by beginners and the majority of recreational skiers, in that it tends to be relatively forgiving, easy to turn upon, and requires less skill to negotiate than powder snow. The name comes from the look of the snow after it as groomed, as it looks like corduroy fabric.

Granular snow

Snow with large crystals, i.e. small pellets. Depending on sun and temperature conditions, it may be wet granular snow — meaning that there is a considerable amount of unfrozen water in it, or loose granular snow, which has no unfrozen water. Wet granular snow will form a snowball; loose granular snow will not. Wet granular conditions are often found in the springtime. Loose granular conditions are generally produced when wet granular snow has re-frozen and then been broken up by snowgrooming apparatus.

Corn snow

The result of repeated daily thaws and nightly re-freezing of the surface. Because of the thaw-refreeze cycle, snow crystal shapes change over time, producing crystal shapes somewhat akin to wet granular, but larger. True corn snow is a delight to ski or ride once it softens in the afternoons.

Ice Cookies/Snow Snakes

Similar to corn snow but much larger. Snow has melted, re-frozen, and been "skiied out", creating hard snowballs of ice- sometimes as big as tennis balls. Skiing in these conditions can be tricky and sometimes dangerous.

Slush

When the sun heats the snow and causes it to become very wet and very heavy. Skiing in these conditions can be difficult.

Ice/Hard-Pack

Skiers and snowboarders typically regard any snow condition that is very hard as "ice". In fact, true ice conditions are comparatively rare. Much of what is perceived to be ice is actually a frozen granular condition — wet granular snow that has refrozen to form a very dense surface. Telling the difference is comparatively easy; if one can get a ski pole to stand up in it, the surface is likely to be more of a frozen granular surface than an icy one — and while it is certainly not as enjoyable as many other snow conditions, skilled skiers and snowboarders can successfully negotiate it. In fact, ice is a preferred condition among racers, in that the surface tends to be quite fast and race course conditions tend to remain more consistent during the race, with fewer ruts developing on the course. Another form of icy condition can be found at higher elevation resorts in the Rocky Mountains and in Europe; direct sunlight can melt the top layers of snow crystals and subsequent freezing produces a very shiny, slick surface.

Crust

A crust condition exists when soft snow is covered by a harder upper layer upon the surface. This crust can be created by freezing rain (precipitation formed in warmer upper levels of the atmosphere, falling into a temperature inversion at which surface temperatures are below freezing, and freezing on contact with the ground), by direct sunlight, and by wind loading which packs down the upper layers of the snowpack but leaves lower layers more or less unaffected. Crusts are extremely challenging conditions.

Dust on crust

A trace of new snow on top of crust. Undesirable.

Spring conditions

A catch-all term ski areas use to describe conditions when numerous different surface types can be found on the mountain — usually in the later part of the season, although the term is sometimes used during an extended midwinter thaw. The term also generally reflects the presence of bare spots and/or areas of thin cover. With spring conditions, the snow is usually firm in early morning (even reaching frozen granular status if left ungroomed), breaking a softer corn or wet granular surface mid-day, and is often very soft and mushy in afternoon (many skiers refer to this type of snow condition as "mashed potatoes", due to its heaviness). In some instances when the snow is untracked, sun baked, slightly dirty, with the consistency of a snow cone, it is called "tecate powder". The speed with which conditions change on a given spring day is directly related to the exposure of the slope relative to the sun. In the northern hemisphere, east- and south-facing slopes tend to soften first; west-facing slopes generally soften by mid-day. North-facing slopes may hold on to their overnight snow conditions throughout the day.

Windblown

A type of snow that forms when powder isn't skied on for a long period of time. It is essentially powder past its expiration date. The consistency is that of a thick and "sticky" powder, that provides lots of resistance; it often is covered by a crust of hard packed snow. It is prone to happening in large, open areas where there is little shelter from the wind. Its appearance often fools inexperienced skiers to believe it is fresh powder.

Variable

"Variable" simply means that all types of snow can be on the mountain, ranging from hard pack to crud. It is usually a secondary classification.