by Tyler Wenzel
When it's early in the season and Mother Nature has brought cold temperatures but no precipitation or we’ve hit a snowless stretch mid-season, most major resorts will be making their own snow. Some resorts, like Mad River Glen in Vermont, have no snowmaking on principle. Many resorts in the western U.S. have very limited snowmaking and some have none at all. Still, it's more likely than not that your favorite ski resort employs some means of generating man-made snow.
What is man-made snow? Is it any different from naturally occurring snow?
First we need to define what “snow” is. The dictionary defines it as:
In other words it’s not much different than rain. In fact the primary determining factor in whether the precipitation falls as rain, snow, sleet, freezing rain, etc. all is based on temperatures in the atmosphere (although other influences like wind and humidity play into the equation). For instance, during the summer months it never snows because from the cloud to the ground it is completely above freezing, thus the water drops stay rain.
For it to snow the temperature has to remain below or very close to below freezing from the cloud down to the ground. Snow is formed as the water vapor that makes up clouds bunches together as it condenses. The air temperature near the cloud will determine the initial shape and size of the snow flake.
· 32-25° F - Thin hexagonal plates
· 25-21° F - Needles
· 21-14° F - Hollow columns
· 14-10° F - Sector plates (hexagons with indentations)
· 10-3° F - Dendrites (lacy hexagonal shapes)
Chart information courtesy of the Chemistry section of About.com
Basically natural snow is water that has frozen into light flaky crystals. If the temperature between the cloud and the ground rises above freezing at some point the snowflakes may melt and then refreeze creating sleet instead of snow. Now we get to man-made snow.
Is man-made snow some type of synthetic chemical or shot from some magic gun? No. In fact for a couple hundred dollars (or less if you happen to have some of the equipment lying around) you could make your very own snow making system. Making snow has two basic components—water and air.
The concept of snow making was first concocted and patented back in the 1950’s. It wasn’t until the 1970’s that it really began to catch on for use in skiing though.
Most industrial snow guns (those that resorts rely on) use compressed air and a high volume of water. But to give an idea of the principles involved, you could replicate the process with a garden hose and small air compressor. The snow gun is basically a nozzle that spreads water out so it doesn’t shoot out like a fountain wreaking havoc on the ski slopes. Feeding that nozzle are two hoses--one with compressed air, the other with water. (A side note: some systems rely on high powered fans to disperse the water rather than compressed air, but in both instances air movement is the key).
The rate at which the water droplets can freeze is why a lot of snow making systems are put on poles along the side of ski slopes. The pole is nothing special—just a standard metal pole with a snow making nozzle on top. However, putting the nozzle up in the air allows the water more time before it hits the ground to freeze and make snow crystals.
This is where a bit of art and science mix in. One cannot simply hook a hose and air compressor into a nozzle and hit the on switch. In fact depending on the weather the amount of water and air being used will vary dramatically. If the relative humidity is high, water is going to freeze slower so there needs to be a higher ratio of air to water. When it is very cold and the humidity is quite low (usually when you get in the teens and below temperature wise) there can be more water dispersed. That is why snow makers will rely on what is known as the “wet bulb” temperature which factors in humidity’s effect on water rather than the standard dry bulb temperature you would see if you looked at a household thermometer. That is why the air temperature can actually be slightly above freezing, but they can still make snow.
The snowmaker’s also have a degree of control over the quality of the snow. Dense, wet snow is not much fun to ski on—but it holds up better to bad weather. So in early season—particularly on high traffic runs—resorts will often blow down a layer of dense snow to build a base on and then put down a layer of “dryer” snow: snow that does not have as dense a structure and is more powdery and fun to ski on.
Snowmaking systems also have to work in conjunction with grooming systems. Generally they will lay down a pile of snow that resembles the tail of a breaching whale—also not fun to ski. After a sufficient amount of snow is put down, the groomers can distribute it across the trail to provide a sufficient base layer to ski on, and hopefully add natural snow too.
One question that comes up is whether or not there is any artificial substances in man-made snow (note that I have refrained from referring to it as “artificial snow” up to this point, because it is the same as the natural product)? Without getting into too deep a chemistry lesson about hydrogen bonds and other various sub-points, snow forms better with something to form around like a piece of dust or a speck of dirt. Blowing dust all over the slopes probably isn’t a great idea, so sometimes resorts may add a completely natural protein to the water to give it something to help adhere to when forming the snowflakes. While it is technically an additive to the process it’s effects are just to help replicate the natural process. Due to the limited space (less than 100 feet to fall rather than thousands from a cloud) snow has to form, it is occasionally used to expedite that process.
So this winter, when you are skiing terrain that Mother Nature was going to keep you from enjoying, give a nod in appreciation of the snow guns and the chemistry whiz who invented their man-made snow.