Natural vs. Machine-Made Snow

One common notion is that machine-made snow is artificial. This is not really the case --
it's actually the same stuff that falls out of the sky, it's just created by a machine rather
than by weather conditions. The machine works very differently than a weather system,
but it accomplishes exactly the same thing. To understand how machines make snow, it's
a good idea to first look at how snow occurs naturally.

Snow comes from water vapor in the atmosphere. Clouds form when the water vapor
(water in gas form) in the atmosphere cools to the point that it condenses -- that is,
changes from a gas into a liquid or solid. The droplets in a cloud are so light that the air
in the atmosphere keeps them aloft. If the droplets get too heavy, they fall in the form of
precipitation. If it is cold enough, this water vapor doesn't condense as liquid water
droplets, but instead as tiny ice crystals. In most parts of the world, rain generally starts
out as snow but melts as it falls through the atmosphere (it is very cold at cloud level,
even in the summertime).

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 naturally-occurring material that help water molecules coalesce.
The nucleators attract water molecules, which reduces their energy to the point that they
form ice crystals. The nucleators in snow crystals are just 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. The collection of individual crystals forms a snow flake. 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.

In nature, we see that snow forms when water vapor condenses in cold enough
temperatures, often around a nucleator, and becomes an ice crystal. So, the main things
you need to manufacture snow are water and cool temperatures. It helps the process along
if you mix a nucleator of some sort into the water supply. The water will already contain
lots of stuff that can act as nucleators, but increasing the count is a good idea because it
ensures that more water droplets will freeze before they reach the ground.


The traditional type of snow gun produces water droplets by combining cooled water and
compressed air. On a ski slope, you'll notice that these guns are attached to two different
hoses that run to air and water hydrant stations, respectively. The hydrants are hooked up
to two different lines which run under the snow or even underground. One pumps in
water from a lake, pond or reservoir and the other pumps in high-pressure air from an air
compressor.

The compressed air serves three major functions:

• It atomizes the water -- that is, disrupts the stream so that the water splits into
many tiny droplets.
• It blows the water droplets into the air.
• It helps cool the water droplets as they fly into the air.

This last step is an added bonus of using compressed air. When air is compressed, the
different air particles are pushed tightly together, which means they don't move around as
much. When the air is released, the particles spread out and move more freely. This
means the particles are using more energy, absorbing heat from the area around them and
thus cooling the air around the water droplets.

Another common type of snow machine is called an airless snow gun. Airless snow guns
use simple nozzles (similar to the ones you find on household spray bottles) to atomize
the water into a fine mist. The water droplets are then blown up into the air by a powerful
fan. The main advantage of this design is that you don't have to hook the snow gun up to
a compressed-air supply -- you only have to provide water and a power source. Some
other snow gun designs actually atomize the water with high-speed fans.

It takes a lot of energy to change water from a liquid to a solid. You have to remove the
water's heat of fusion, the large amount of heat energy required to change ice into liquid
water at 32 F (0 C). If it's cold enough, the natural conditions outside will be sufficient
for freezing the water; but if it is only a little below freezing, you may need additional
components to help the process along. Some snow machines have special cooling units to
speed the freezing process when the natural conditions aren't cold enough to do the job.

To give the water enough time to freeze before it falls to the ground, many resorts use
snow gun towers. These are simply sturdy poles that elevate the snow gun above the
slope. Another advantage of this set-up is that the snow guns can be less disruptive to
skiers. And the snow falls from above, as it would naturally.

Snow-Making Conditions

As we've seen, the main job of home snow-making machines is to do the work of snow-making clouds that occur naturally in the atmosphere. These machines do not make snow under just any conditions. However, you need to have the right kind of ground weather, just as
you need the right kind of ground weather for natural snow to make it to the earth and
then stick. To figure out when to make snow, and to make sure they get the right kind of
snow, ski resorts depend on the expertise of experienced snow machine operators,
commonly called snow-makers.

So 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 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 or solid water cools itself by
evaporating some water as water vapor. This releases heat, and so lowers the energy level
in the water. When there is more water vapor 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 cools more slowly when the humidity is high, and more quickly
when the humidity is low.

For this reason, humidity is a very important factor in determining snow conditions. If the
humidity level is low enough, you can actually get snow even when the dry bulb
temperature is several degrees above freezing. If the relative humidity is 100 percent,
then the wet bulb temperature and the dry bulb temperature will be exactly the same. But
even if both are at the freezing temperature, you might get rain instead of snow because
the air saturation slows the cooling process down so much.

If the temperature is around 30 F (-1 C), you need a fairly low relative humidity (less than
30 percent) for good snow-making conditions. If the temperature is less than 20 F (-6.7
C), you can make snow fairly easily even if the relative humidity is 100 percent. A
temperature in the teens is ideal for snow-making.

Information provided by How Stuff Works. You can view the complete article at http:travel.howstuffworks.com/snow-maker.com.

Southern Snowman 
Mt. Roundtree  Cary, NC 
sales@southernsnowman.com 
919-971-6341 

Bringing Snow to the South, One House at a Time