SNOWMAKING

 

Snowmaking is the process of creating snow by dispersing minute water particles and pressurised air into a significantly gelid (cold) atmosphere. This produces a snowflake lattice structure that is similar to natural snow. By regulating water & air content, snow can be deliberately made from light powder to wet base snow, and to withstand higher temperature or significant precipitation before melting.

 

Snow is made by forcing water and high pressure air through nucleating nozzles in a snow gun. The basic objective of snowmaking is to atomize the water into droplets, blow the droplets up into the air and allow them to substantially freeze before they contact the ground. The smaller the droplets, the faster they freeze.

 
The atmospheric factors affecting snowmaking are;

 

A critical factor in snowmaking is the "wet-bulb temperature". This is the temperature a wet thermometer will be cooled to if air is blown over it - a condition similar to that which the water droplets are being exposed to during snowmaking. When the air temperature is close to freezing, the wet-bulb temperature becomes important. In fact with the right equipment, snowmaking can take place at +4 degrees Celsius if the relative humidity is low enough to yield a wet-bulb temperature below 0°c. Evaporation causes cooling. This principal is used in evaporative coolers, or on the evaporative water bags you used to see on the front of 4wd's to cool water.


Guns are normally aimed with the wind rather than into the wind. This will allow snowmakers to add more water to the gun and make more dry snow, and also helps to reduce ice build up. Aiming the gun up at about 35 degrees will allow snowmakers to put more water through the gun and will allow greater coverage. On windy days some snow will be blown off the trails, however it is an illusion that all of the snow is being wasted. A few tiny droplets break away from each main drop during the atomisation & spraying process. These tiny droplets are very reflective, more so than the larger heavier snow crystals that end up on the trail and it only looks like all the snow is blowing away.

 

Snowmakers should let the snow set before it is groomed. Air pockets will be squeezed out of the pack when groomed if the snow is not allowed to set first, creating an icier pack. Man-made snow is mostly more dense than natural snow, it doesn't need to be compacted. The first 24 hours is the most important. Ice is continually sublimating (evaporating) and recrystalising into a bonded mass.  This is where layering the snow with a dry layer on top can help reduce the need for grooming. Many resorts, in their efforts to create a more resilient snow pack groom too soon causing a layer just below the snow surface to become icy and the ski run will lose its appeal earlier in the day.

 

Icy areas are first covered in wet snow to cause the layers to bond. Wetter snow is also more resilient. The snow can be made drier throughout the night by the snowmakers by increasing air pressure or decreasing water volume. Just as the wind dries your clothes, the added air at pressure causes some evaporation, and in turn causes cooling. Wet snow is created more early in the season to create a base, or on icy or wind exposed locations.

Tower-mounted guns are normally more efficient than guns on the ground, and variable height tower guns are the most efficient of all. Height allows more time for the droplets to freeze, and and a better ratio of air to water can be obtained. Varying the height can allow for a better coverage of specific locations during windy periods.

 

All in all man made snow is often regarded by the resorts as better snow. It lasts longer, is easier to work with, and can be made on demand if the temperatures are right. A well made pack with dense snow on the bottom and a dryer surface on the top is also enjoyed more by most riders. An Australian resort has already extended their average season by almost a month by using this technology.

 

Mick Eyers