Snowmaking Made S i m p l e A summary of the ART OF SNOWMAKING Just for FUN, take the Do you know? quiz! Skiing Wisconsin www.skiingwisconsin.com
Ski Areas Can Make Snow But Nature Does it Best The Nature-made Snowflake Snow is precipitation in the form of crystalline water-ice. Snowflakes form when tiny super cooled droplets freeze as a few of the molecules connect in hexagonal prisms. The freezing process is helped by dust and other biological particles in the air which Nucleate the process allowing the freezing to take place at a higher temperature. Sometimes, instead of a flake, snow will fall in the form of a small bee-bee due to melting and re-freezing. This type of snow is called Graupel, Ice Pellets or Snow Grains. It is still snow and on the ski hill is just as much fun. Snow forms in the clouds well above the earth s surface. Temperatures are lower there which is why it can snow while the temperature in your yard is near or even above 32 degrees. Why are some snowflakes six sided or Hexagonal in shape? What is Graupel Snow? Can nature produce snow when the temperature at the earth s surface is above 32 of? How does dust or biological particles help in the formation of natural snowflakes? What scientific process helps in the freezing of the water droplets? The Heat Factor Water is a unique material; it expands when it freezes making it less dense. That is why your ice cubes float and last a long time. Liquid water always has a certain amount of heat to keep it liquid. Therefore water must be cooled, removing this heat, in order for water to freeze. A large amount of heat removal (cooling) is required in snowmaking.
The water molecules slow down as this heat is removed allowing them to align in the familiar hexagonal crystals. These will stick together in the formation of snowflakes. During snow formation and the snowmaking process, this heat is dissipated into the air, the water droplets cool as they fall to the ground. If there is enough hang time the droplets form snow before they land. What happens to liquid water as it freezes? Why do snowmaking systems use a cooling pond to cool their snowmaking water? Why is Hang Time important? The Nucleation Factor Oddly enough, water doesn't automatically freeze at "freezing temperature" 32 degrees Fahrenheit / 0 degrees Celsius. You have to cool pure water to a much lower temperature (as low as -40 F / -40 C) for it to lose enough heat energy to change form. Usually, however, water in a cloud does freeze around 32 F / 0 C because of the work of nucleators, tiny bits of naturallyoccurring material that help water molecules coalesce. The nucleators attract water molecules and help them stick together and reduce their energy to the point that they form ice crystals. These nucleators in snow crystals are small dirt bits, bacteria and other material floating around in the atmosphere. Water condenses onto the nucleator, which becomes the nucleus -- the center -- of the snow crystal. As the snow crystal moves around the cloud, more water particles condense onto it and freeze into crystals. This collection of individual crystals forms a snowflake. As the snow flake grows heavier, it falls toward the earth. If it is cold enough the whole way down, the flake will still be frozen when it reaches the surface and accumulates in your back your and on the ski slopes. How do dust particles in water help the freezing process? What do snowmaking crews do to help the water freeze? How would adding Nucleators to water help in snowmaking?
The Evaporation Factor and Relative Humidity How do snow-makers determine if the conditions are right? It turns out they need a lot more information than they can get from an ordinary thermometer. Standard thermometers measure the dry bulb temperature of the atmosphere; but the most important factor for snow making conditions is the wet bulb temperature. The wet bulb temperature is a function of the dry bulb temperature and the relative humidity, the amount of water vapor in the air. Liquid water cools itself by evaporating some water as water vapor. This is a natural cooling process much like your body feels cooler when you perspire. This releases heat, and so lowers the energy level in the water. When there is more water vapor (moisture) in the atmosphere, water or snow* can't evaporate as much because the air is already saturated with water to a high degree. Consequently, water then cools more slowly when the humidity is high, and more quickly when the humidity is low. (* Snow actually does evaporate through a process called sublimation. ) For this reason, humidity is a very important factor in determining snow making conditions. When the humidity level is low enough, you can actually form snow even when the dry bulb temperature is several degrees above freezing. If the relative humidity is high, say a foggy 100 percent, then the wet bulb temperature and the dry bulb temperature will be exactly the same. Even if both are at the freezing temperature, you might have rain instead of snow because the air saturation slows the cooling process down so much that freezing of the water particles will not happen. Why is it important for snowmaking to have low relative humidity condition? How does the evaporation process help in the freezing of water molecules? How would the size of the water droplet affect the freezing process? Snow Making is an Art in Wisconsin Man-made Snow Comes Close to Nature s Snowflake The Snowmaking Systems The Reservoirs All snowmaking systems start with a water supply; usually a nearby natural or man-made pond or reservoir. It is important that the reservoir be large enough to adequately supply the pumping system. Only water makes snow and it starts with a large reservoir near the pumping station. Water stored in the pond is cooled as it is exposed to the cold air temperature. Some ski areas aerate the pond to keep the surface open, cooling the deep water below the surface where it is drawn for snowmaking. These open surfaces are dangerous. That is why it is important to stay off the thin ice of snowmaking ponds. Do you Know? Name two advantages of Aerating snowmaking ponds.
The Pumping Station Water is pumped from the pond using large turbine pumps through underground pipes that take the water to all the ski runs. Hoses are connected to the hydrants located on the side of the ski runs and then connected to a series of different snow guns. One of the major costs in snowmaking is the electricity needed to run these large turbine water pumps. These turbines pump many gallons per minute to the slopes through miles of large diameter pipes. The water does not freeze in these pipes because it is moving very fast. But if the water pipes are on the surface next to the ski runs, those pipes must be drained when the system is shut down Do you know? Once the water leaves the pump house, pushed by the pumps, where does it go? The Man-Made Snow Man-made snow will go through the same freezing process as natural snow. Snow making crews will place snowmaking machines around a ski slope, use them to spray small water droplets into the air, expose them to a nucleation particle added to the water and watch them freeze into a local man-made snowstorm. It takes a large amount of water to make snow. Water is stored in a large reservoir near the pumping station. Most systems use 200,000 gallons to make one foot on one acre (one acre-foot) of ski slope. Many ski areas in Wisconsin use over 50 million gallons each year to cover all the slopes with over four feet of snow. This is enough snow to fill Lambeau Field over the top like a snow cone. The Snow Guns or Snowmaking Machines There are three types of snow guns. Airless or Water Only snow guns, Air/Water snow guns and Fan Guns sometimes called snow Cannons. Regardless of the type of equipment used, all snow making machines need to spray the water into the air as small water droplets. Airless or Water Only snow guns will use high water pressure through small nozzles stationed high above the ground to give the water particles enough hang time to freeze into snow. The high pressure also helps atomize the water into small droplets and because of the rapid drop in pressure as the water leaves the nozzles there is a cooling affect to assist with the snow flake formation. Air/Water Snow Guns use a combination of high pressure air and high pressure water to break the water particles into smaller droplets. Here again because the water leaves the nozzles in a small droplet size, it will freeze into snow before it lands on the ground.
Fan Guns or Cannons use the same concept to break the water into small droplets but they add a fan to blow the droplets high into the air to add Hang Time allowing the formation of larger snowflakes. Fan Guns also add a high pressure mist to act as nucleators to further help the droplets freeze into snowflakes. What are the three types of snowmaking machines? Describe which snowgun would make the most snow and why. Which type of snowgun would create the largest coverage on the slopes? How does the Nucleation Process help the fan guns? The Final Step Snow Grooming It is very difficult to evenly coat the entire surface of the ski runs with the snowguns only. Snow falls from the snow making machines under its plume into piles of fresh snow. Snowmakers then allow time for the snow pile to cure when each of the snowflakes harden and dry, freezing more solidly.
The snow grooming process then starts with using large grooming tractors to push the piles around the slope, smoothing the snow surface into and even coating over the entire width of the ski slope. Finally, the same tractors pull a powerful Tiller and Snow Comb to finish the snow surface into a smooth corduroy surface. Tractors are powerful enough to groom even steep slopes while traveling either uphill or downhill. On the steepest slopes, specially equipped Wench-cats connect a strong wench to a fixed object uphill to help pull the grooming tractors up the slope. Some tractors are built with narrow tracks to groom the narrow chutes for snow tubing. These powerful tractors cost over $350,000 each. Ski areas invest large sums of money in tractors to meet the needs of all their guests whether they are skiers, snowboarders or snow tubers. Why is it necessary for ski hill operators to use snow grooming machines? What creates the corduroy surface behind the snow groomers? Why would tubing operations use a narrow grooming tractor? And you thought it was easy fooling Mother Nature. Ski areas all over the globe supplement their annual snowfall with their own snowmaking systems. This is especially important in Wisconsin where the average natural snow fall is just 46 inches. Snowmaking is even more important in El Nino years which offer limited natural snow and small snowmaking windows of opportunity. Even if there is no natural snow in your back yard, ski areas across the state will make snow whenever the conditions allow, usually starting at around 28 of. (Ahhh but don t forget the humidity factor. Wet bulb could be lower.) While it seems a complicated process, ski areas have converted their methods to the most efficient and environmentally friendly systems available. Most snowmaking pumps
are highly efficient variable frequency electric motors and environmentally friendly snow guns. Even the latest technology in emissions and fuel-efficient grooming tractors are used. Ski areas simply borrow many gallons of water from their reservoirs and return the water to their storage ponds, nearby streams and water tables every spring during the snow melt-off. So next time you are sliding down the slope whether there is snow in your yard or not, you know that while you slept ski area operators have been busy preparing the ski runs, snowboard parks and tubing areas for your family fun. Get to your local Wisconsin ski area; enjoy the day and find a snowmaker to thank. Skiing Wisconsin