WHISPERGUN

Whisperguns™ outperform other snowguns and are available on towers, sleds, and tripods.

Whisperguns™ are fully self-nucleating and do not require Snomax® or any other nucleating agent to function in warm weather.

Whisperguns™ produce better quality snow. It has a better texture and is easier to control.

WhisperTowers™ are inherently portable.  When snowmaking is done, they can disappear. Your ski area does not have to look like Grand Central Station.  After all, the great outdoors is what skiing is all about.

WHISPERSLED™

The WhisperSled™ conveniently converts from the running position to the towing position with a tongue that helps lift the sled out of the snow when it is extended.

WHISPERTOWER™

A WhisperTower™ is light enough to be portable. It has the ideal height of 12′ and simply sockets onto a 3″ pipe inserted into the ground. It is high enough to run at peak efficiency and short enough to limit snow loss off-trail. When snowmaking is done, the trail is back to its natural state.

THE TECHNIQUE OF SNOWMAKING

The basic objective of snowmaking is to atomize water into droplets, blow the droplets up into the air, allowing them to substantially freeze before they contact the ground (hopefully on the ski trail). The smaller the droplets, the faster they will freeze. Therefor on a warm day you will be running the gun leaner, producing finer droplets in order to make snow.

The atmospheric factors affecting snowmaking are (in order of importance):

Temperature

Relative Humidity

Wind Speed

Wind Direction (relative to the gun)

Altitude

Solar/Infrared Radiation

Temperature, relative humidity, and altitude can be combined into a single factor called “wet-bulb temperature”. This is the temperature a wet thermometer will cool to if air is blown over it – a condition similar to what the water droplets are being exposed to during snowmaking. When the air temperature is near freezing, the wet-bulb temperature becomes very important. In fact with the right equipment, snowmaking can take place at 40 degrees Fahrenheit (+4.4 degrees celsius) if the relative humidity is low enough to yield a wet bulb temperature below 32 degrees Fahrenheit (0 degrees celsius). This may seem a bit bizarre, but the weather in the Western US frequently allows this. On one day I personally made snow at 50 degrees Fahrenheit in Utah. The atmosphere was extremely dry and so was the snow.

The key to efficiency is the air to water ratio at a given wet-bulb temperature. The best way to predict snowmaking weather is to watch the dew point upwind if the surrounding terrain is frozen. The dew point is that temperature at which water will start to condense out of the air. When the terrain upwind of you is frozen (including any body of water), or unless it gets warm enough to melt the snow, the dew point of a large air mass tends to be fairly constant throughout. This means that if you are making snow at night, when the sun comes up in the morning, the temperature rises and the relative humidity drops. The wet bulb temperature goes up slowly and the dew point is constant throughout the day and night. You can often continue to make snow without change unless the temperature rise is too great. The real change in snowmaking weather is when a new air mass moves through and the dew point suddenly changes. Of course if the temperature goes up enough to melt the surrounding terrain, the dew point will also go up and snowmaking conditions will deteriorate.

Don’t try to fight the wind – you’ll lose. Aim the gun with the wind. You’ll be able to add more water to the gun and make more, dryer snow. If necessary, add an extra length of hose to get the snow where you want it. Start making snow with the hose fully extended, periodically pulling the gun backwards in a zigzag fashion during the night/day until you are finished. this will cause the snow to be layered and evenly distributed. If you do make wet snow it will be covered with dry snow each time you pull the gun back, leaving a perfect surface when you’re done. If there is no wind, or if the wind is blowing in line with the trail, place the gun in the center of the trail and aim the gun up or down the trail with whatever wind there is. This will allow you to build broad smooth mounds of snow in the middle of the trail where it belongs. The skiers will spread the snow out to the edges for you.

Anticipate the wind characteristics of your mountain! Does the wind direction tend to change as the sun sets? If you can predict where the wind will go you will save yourself a lot of work. Watch the wind when testing snow quality as it falls on your arm. A sudden gust can change the apparent snow quality from one second to the next. In very warm weather or windy conditions the only valid measure of snow quality is to test what has actually fallen on the ground. Grab a handful of snow and squeeze it to see how much water there is in it.

Provide rain gear to snowmakers – it pays! To maximize a gun it should be adjusted wet and then carefully throttled back until the desired snow is produced. It is not fun to be soaked to the bone on a cold night. If snowmakers are not wearing rain gear, they aren’t going to want to test if the snow is wet, therefor they are likely to err on the dry side – that is a lot more expensive than rain gear.

Aim the gun up at about a 35 degree angle. This allows you to put more water to the gun and more than compensates for any extra loss off-trail. It often appears that more snow is lost off-trail than actually is. During atomization of the water, as each main droplet is formed there are also two very small droplets formed due to a harmonic when the main droplet breaks off. These tiny droplets tend to be reflective and noticeable although they are only a very small portion of the snow mass produced. Frequently they are carried upwards by convection and disappear altogether. Fortunately they are not significant, the vast majority of the snow is falling near the gun.

Try to let the snow set up before grooming if possible. Man-made snow is dense enough, it doesn’t need to be compacted. The first day is the most important. Ice inside the snow mass is continually sublimating (evaporating directly from a solid) and recrystallizing into a bonded mass. Grooming too soon will compress the snow, squeezing out air pockets if the snow is not allowed to set up first. This is where layering the snow with a dry layer on top can help reduce the need for grooming.

When trying to cover ice, start by making wet snow then cover it with dryer snow. This bonds the snow to the ice and builds a durable base that won’t be worn off as quickly. You should also make damp snow when the wind is blowing hard enough to drift dry snow. If there is natural snow drifting, you can trap it on the trail by making damp snow, producing large piles.

Small output snowguns tend to be more efficient than large snowguns of similar design. This is most obvious in warm weather when the water to a large gun has to be throttled way back due to the limited cooling effect of the air within its plume. This is one of the reasons the Whispergun™ has a wide pattern – to maximize cooling.

Large systems should be designed to run a gun on every hydrant of a given trail simultaneously. This allows you to cover a complete trail overnight efficiently without continuously moving guns. This also makes smaller guns more practical.

Tower mounted guns can be more efficient than guns on the ground – if they are not too close to a tree line. The greater height allows more time for the droplets to freeze, therefor more water can be put to the gun and a better air/water ratio obtained. The first 10-12’ (3-4 meters) is by far the most important for cooling purposes. You can gain about 25% on the air/water ratio with short towers. Taller towers are only necessary if the output of a gun is poorly nucleated. You also lose more snow off trail with tall towers when the wind is adverse.

Placement of the towers is important. If a tower is poorly placed, the snow lost into the woods will be greater than the gain in air/water ratio. Some tower designs are so poorly nucleated that they need to be significantly higher than 10-12’ (3-4 meters) in order to work at all. You may need to incur the cost of injecting a nucleating agent like Snomax™ to make them work at any temperature above your water’s natural nucleation temperature.

Whisperguns™ do not require a nucleating agent, making better snow at lower cost. Test your water to find out what its natural nucleation temperature is. Natural bacteria, clay particles, spores, and other particles have a significant impact on the temperature your water is likely to freeze at quickly enough for snowmaking. The test should NOT be done indoors during the winter as indoor humidity is consistently low during the winter. It should be done outdoors in mild weather under both high humidity and low humidity conditions.

We have found that most nuclei work better in low humidity conditions and often not at all in high humidity conditions. This is where a self-nucleated gun like a Whispergun™ excels. When you do the test, pay particular attention to the amount of time it takes for identical sized droplets to freeze at a constant temperature, as this is the parameter affected by humidity. In snowmaking you need those droplets to freeze quickly. This means that when you test your water with a commercial nucleating agent, you may find, for example, that you do not want to inject the agent during the night when the humidity is high, but instead inject just at sunrise when temperatures start to rise (and the relative humidity starts to fall). You could save real money by paying attention to the humidity. There is more about nucleation in the NUCLEATION section.

Have an extra set of guns. Frequently this improves system efficiency by 25% if a ski area desires to change trails frequently. The second set of guns can be set up in advance of a trail change, greatly reducing downtime while you change trails.

A good air-to-air aftercooler/demister for the compressed air is worth its weight in gold. The dew point of the compressed air should be reduced to within a few degrees of the outside air to minimize rime ice within the air hoses. Changing hoses is not fun and very inefficient in the long run. Choose an aftercooler with at least twice the capacity you think you need.

Fergus S. Smith

NUCLEATION

Without nucleation, a water droplet would never freeze before it hit the ground. Snowmaking requires crystallization of water droplets in the air before they hit the ground, otherwise you get a sloppy mess and clear ice. Nucleation is essential to that crystallization. When water is very pure, it is very slow to freeze.

We can see that clearly from the icing that occurs on airplanes flying through clouds at temperatures like 28 F/ -2 C. The water droplets in those clouds are frequently ready to freeze on contact with the airplane wing. If they are sparse and small enough, they can flow around the wing harmlessly. If they are a little larger, they will hit the wing ballistically and freeze instantly forming pebbly rime ice. If they are yet larger and abundant, they will splat on the surface and produce clear ice. Those supercooled (subcooled) droplets can be stable in clouds as liquid droplets for hours, even days. Large jet aircraft have heat from the engines to melt it, so it isn’t dangerous to them, but light aircraft can have a serious problem. If they can’t get out of the icing layer of clouds, they are going to go down. In the mountains that can be a particularly serious problem.

Nucleation is a common phenomenon throughout Chemistry and Physics. It is important in many fields from meteorology to metallurgy to glass, ceramics and beyond. Many things we take for granted would not work without it.

It is simply faster and easier to start with a significant chunk of something you want to produce, than to start with the individual molecules one by one. If you want to build a house, don’t start with grains of sand.

Water has unusual characteristics and water molecules are of course very small. Water behaves like a much larger molecule than it is. Methane (natural gas) is a molecule about the same size as water, yet it is a gas at room temperature and doesn’t condense until you reach -258 F (-162 C).

So why does water behave like this?

It is due to a phenomenon called “Hydrogen Bonding“. Water molecules are very strongly attracted to one another. The hydrogen atoms on each water molecule are attracted to the oxygen atoms on neighboring water molecules. They tend to form clusters of about 7 water molecules on average. This is why water boils at 212 F/100 C instead of -250 F/-160 C. This clustering also delays water molecules from rearranging easily into the neat rows and columns of a crystal. At the same time, it is hydrogen bonding that allows water to be a liquid at room temperature and to crystallize below 32 F/0 C in the first place. Otherwise it would be a gas like methane.

There is another reason water droplets don’t freeze quickly. If water is very pure, you can cool it to -40 F/-40 C and it can still be a liquid. The reason is simply due to the incredible number of water molecules in a droplet of water. There are about 10,000,000,000,000,000,000 water molecules in a single droplet of water. When individual water molecules start to form a crystal, they are so small that it can take a very long time for the crystal to grow to a significant size.

This is why, if you want a droplet to freeze quickly, you need to start the crystallization on a small bit of something with the right shape and surface chemistry. If that “bit of something” is visible under a microscope, it is vastly larger than a water molecule and has far greater area upon which crystallization can occur.

However, once crystallization starts, crystallinity is the favored structure below 32 F/0 C. Taking that favorable crystalline structure saves a tremendous amount of energy. When that energy is released it has to be transferred out of the water droplet to keep it below 32 F/0 C to continue the freezing process.

There are basically two ways to nucleate a water droplet to cause it to freeze within a reasonable amount of time. Nucleation can occur due to foreign particles dispersed WITHIN the droplet, OR a nucleus like another ice crystal can become ATTACHED to the outside of the droplet.

The ideal nucleus to freeze water is ice itself. It can nucleate crystallization when the water droplet is just below 32 F/0 C. It has exactly the right shape and surface chemistry for water molecules to attach to (water likes itself). If the water droplet is being cooled adequately and the crystal nucleus is large enough to begin with, the seed crystal can grow fast enough to freeze the droplet before it hits the ground.

There are natural nuclei in the environment that can initiate crystallization of water at temperatures a few degrees below 32 F/0 C. Natural nuclei are very abundant at 12 F/-11 C. Even testosterone is effective as a nucleating agent for water but it is too expensive to be practical and you really wouldn’t want to spray people with testosterone.

Some years ago a fellow at the National Weather Service became curious why there was often hail in a mountain range in Canada. He found that there was debris from rotting leaves that contained the natural bacteria Pseudomonas Syringae. That debris was being blown up into the air, frequently causing hail.

It is actually the proteins in the bacteria that help form water crystals. That’s why you can kill the bacteria and activate it by freeze drying. Proteins are composed of amino acids. Some amino acid sequences can exhibit hydrogen bonding in a pattern that is easy for water molecules to crystallize onto. Commercial nucleating agents take advantage of the ease and low cost of growing the bacteria. It isn’t as effective as actual ice nuclei, but it can work. More about Pseudomonas Syringae can be found here. https://en.wikipedia.org/wiki/Pseudomonas_syringae

Some people think that cloudy water with clay particles is good for snowmaking. It actually isn’t the clay. Most clay particles are rather poor nucleating agents and of little value. Using dirty water also has the side effect that when Spring comes, the dark clay particles absorb sunlight and cause the snow to melt faster. It is mostly organic matter that is helpful for nucleation. Even when water looks clean, it really isn’t.

The actual mechanism of nucleation in a compressed air/water snowgun depends upon the surface of a water droplet cooling to 32 F/0 C before the ice nucleus bumps into the droplet. If the surface of the water droplet is above that temperature the ice nucleus will melt. If it is below that temperature, the crystal will grow. To be sure that you get crystallization, you want a lot of ice nuclei. Fortunately that’s easy if you do it right.

If you could see inside the compressed air hose, you would see a sort of fog flowing toward the gun. That fog of droplets is caused by the cooling from the outside of the hose. When that enormous amount of tiny water droplets goes through the snowgun nozzle, the compressed air expands and cools, flash freezing those tiny droplets and water vapor. Those ice crystals aren’t noticeable, but they are what cause the much larger droplets to freeze. They actually amount to a very small fraction of the total water volume, but without them you get rain.

Nuclei that are not composed of ice use a different mechanism to nucleate a water droplet. It is why synthetic nuclei dispersed inside the water droplet do not help much in high humidity. They need to float outward to the surface of the water droplet and be exposed to the atmosphere. If there is a thick film of water on the surface of the protein nuclei, the clustering of liquid water molecules interferes with the initiation of crystallization.

Clustering of water molecules is why synthetic nucleating agents dispersed within the water do not work well in high humidity. The surface water needs to first evaporate before nucleation can be effective. If the rate of water flow is low enough and the droplets are dropped from enough height, they will perch on top of existing ice and freeze due to nucleation by the existing snow cover on the ground. This is why they often produce a styrofoam like surface. Fortunately that surface can be groomed to make an adequate ski surface, but grooming also costs money.

It is the same reason frost forms so easily on objects like your car windshield. It crystallizes directly from gaseous water vapor onto the surface. Liquid water clusters do not get a chance to interfere with crystallization and the RADIANT temperature of the sky above is also very cold, typically -15 F/-26 C even when the AIR temperature can be above freezing. On a clear, calm night, it is that cold sky that causes the top surface of leaves facing up to become much colder than the air temperature and freeze. The bottom side of the leaf is facing the ground and bathed in air, so it stays warmer. That cold sky is why your tomato plants freeze so easily. That’s why placing a cloth over them can prevent them from freezing. The top side of the cloth gets cold, but the bottom side facing the warmer ground remains warmer. You can see it clearly with an infrared thermometer.

Proteins can also have the opposite effect of nucleation, acting like antifreeze. Some fish contain proteins that allow them to survive being trapped in frozen water. Note that the needles of evergreens stay green through the Winter. When it is cloudy in the Fall, the foliage develops less red in its display of colors. That red pigment complex is proteinaceous, likely delays nucleation, and protects the leaf from freezing on a clear, cold night. That may be surprising, but plant and bacterial proteins are undoubtedly a factor in poor nucleation of surface water used for snowmaking. There is a segment about windshield ice explaining that very cold sky in the Eureka! section.

There’s a lot more to be said about nucleation, but those are the highlights.

Fergus S. Smith