School seems a world away when your skis cut cleanly through a thin coating of snow, sending up a shower of fresh, white powder. But what if the temperature isn’t cold enough for snow to form? Could nature really sabotage the perfect ski holiday? Fortunately, today’s technology is so advanced that Mother Nature is no longer in complete control of snow distribution. Resorts use snow machines to extend the length of the season, while ensuring that snow is the right consistency for skiing and snowboarding.
Snow is naturally produced as cloud temperatures drop. Water vapour condenses into droplets, which remain in the atmosphere until they grow too large. Water doesn’t actually freeze at 0°C, but at much lower temperatures. In clouds, small pieces of dirt, bacteria, and other small particles called nucleators cause water particles to group together. These particles expend energy in their attraction to nucleators, causing them to cool until they form ice crystals. As the crystals drift within the cloud, more water molecules gather around them to form a snowflake, which begins to fall as it gets larger and heavier. The drop will remain a snowflake, provided temperatures remain cold enough. Otherwise, the drop falls as rain.
The snow produced by machines is the same as naturally-produced snow. Both processes require only water and cold air. Traditional snow machines, or snow guns, have two hoses: one connected to a water supply, and another that provides compressed air. This air pushes the water particles tightly together, reducing their ability to move. When the air is released, the particles spread, and can move more freely. As they are scattered through the air, they use up energy and absorb heat from their environment. Some resorts use airless snow guns, which employ nozzles to atomize the water stream into a mist. A powerful fan located inside the gun then blows the droplets into the air. This design is often preferred, as it doesn’t require a supply of compressed air.
Although these powerful machines are credited with longer ski seasons and a greater variety of trails, there are limits to their snowmaking abilities. Just as particular ground-weather conditions are needed for natural snow, snow machines can only produce snow at certain temperatures and humidity levels. The most important factor in snowmaking is the wet bulb temperature. Also known as the relative humidity level, it determines the amount of water vapour in the atmosphere. When there is more vapour in the air, water or snow cannot evaporate easily, as the air is already saturated with water. As a result, it takes longer for water to cool under high humidity conditions, making it difficult to produce larger quantities of snow. Ideal snowmaking conditions necessitate temperatures between -10° and -20°C and low levels of humidity.
Snow machine operators have to consider more than just the environmental conditions. They must also monitor the proportions of water and air in accordance to the needs of the slope. The density of snow is chiefly determined by the size of water droplets created by the gun. Dry snow has a low amount of water, which makes it the best snow for skiing. Wet snow, which has a higher density, is used to build a foundation on the trails. It is produced twice a year to create depth, while trails are regularly coated with dry snow throughout the season.
Since temperature and humidity levels vary greatly across the slopes, snow makers must pay careful attention to the weather, and adjust each machine accordingly. Many ski slopes use central computer systems that are connected to weather-reading stations. These computers determine the best combination of water and air based on the data recorded.
Snow making technology is more widely used than you may think. Hollywood producers, agricultural engineers, and aircraft designers all depend on this technology. Although they require a great deal of power and water, snow machines are relatively easy to operate. So the next time you’re sitting in the chalet after flying down the slopes, you can impress your friends with your knowledge of the science of snow.
