Snow. When you really think about it, it’s the one essential component to our
sport. Lifts? You can hike. Mountains? There’s always Nordic skiing. Skis? It
wasn’t that long ago that they were fashioned out of barrel staves. It
also wasn’t that long ago that skiing was less than reliable.
The actual origins
of snowmaking have been disputed for years, but conventional wisdom states that
Walt Schoenknecht of Mohawk Mountain, Connecticut (and later Mount Snow, Vermont)
developed the first commercially viable snow gun during the 1950’s. Another
school of thought gives credit to the process of agricultural spraying to prevent
citrus freeze. However it arrived, snowmaking is here to stay, even at traditional
natural snow powerhouses like Alta or retro areas like Mad River Glen, both
of which use snowmaking to touch up high-traffic areas. These days, when you
plan a ski vacation, you can be reasonably assured that skiing will be possible
when you arrive at your destination. As much as many of us hate snow from hoses
when compared to natural fluff, you can thank the snowmaking process for your
This article isn’t devoted to history, though. We’ll explore the art and science
of making snow with the latest techniques and technology.
IT’S JUST AIR AND WATER, RIGHT?!
managers wish that it was that easy. Yes, those are the two basic components,
but the methods to turn those into an enjoyable ski surface are complex and
vary widely. You can make your own homemade snowmaking
system, but it’s not simple.
First off, let’s dispel a myth: it’s not "artificial snow." The use
of that term by skiers and non-skiers alike really gets under my skin. A more
correct term would be "man-made snow." Natural snow is formed when
the water vapor in clouds condenses and falls to the ground. If this condensation
occurs at temperatures which are cold enough, the condensed moisture forms a
tiny crystalline ice structure. Man-made snow is created in much the same way:
tiny water droplets freeze into crystals before falling to the ground as snow.
The crystal structure is quite different, however. Natural snowflakes have
six tiny arms, known as dendrites, much like what appears in the background
image of this article. Man-made snow, however, forms a compact six-sided structure,
allowing it to pack more densely and retain less air. This helps to explain
why man-made snow skis more firmly to the touch, and retains its durability
more effectively than does natural snow.
The real meat of the issue is how to create these water droplets. Snowmakers
use two different types of systems, water/compressed air systems or "airless"
systems, to accomplish their objective.
TRADITIONAL WATER/COMPRESSED AIR SYSTEMS
Early snowmaking technology, such as that used by Schoenknecht, was a marvel
of ingenuity and good fortune. Fashioned from standard plumbing fixtures of
the day, it’s a wonder that they were as effective as they were. Snowmaking
technology has developed so rapidly in recent years that even equipment a decade
old is considered antiquated.
In the traditional system, water is forced through a nozzle under high pressure
by compressed air. You’ve probably observed two pipelines alongside a ski trail
serviced by snowmaking; one is to carry the water, and the other to transport
compressed air. This compressed air serves two purposes: to atomize the water
into tiny droplets, and to thrust the moisture skyward to allow it to cool and
freeze before falling to the surface as snow. Simple, right?
The exact mix of water and air determines how wet or how dry the resultant snow
will be, or even if it will have time to freeze at all. In the old "jacket
sleeve" test, snowmakers would stand in the gun’s fallout area and raise
their sleeve to have a look. If the snow bounced off their sleeve, it was dry.
If it stuck, it was wet. The snowmaker would adjust the mix at the hydrant which
serviced each gun.
The proper mix of air and water is dependent upon two factors: temperature
and humidity. These factors can vary dramatically at different points on the
mountain, or even from one snowgun to another. “To make snow is simple,” says
Slavko Stanchak, Director of Snowmaking Engineering at American Skiing Company.
“But, to consistently make good snow that is also consistent from the top of
the mountain to the bottom, that’s damn hard.”
Due to the complicated relationship between temperature and humidity, it’s
actually possible to make snow at temperatures above freezing. Likewise, on a
humid day, it may not be possible to make snow even though the thermometer on
your ski jacket indicates that it’s well below freezing. Let me explain.
When you look at a traditional thermometer, you’re looking at what meterologists
refer to as the "dry bulb" temperature. Remember how hot you felt
on an 80-degree summer day that was also very humid? It certainly felt hotter.
Hotter even than a dry, 90-degree day the week before. You body utilizes "evaporational
cooling," whereby you are cooled by moisture in the form of perspiration
evaporating from your body. If the ambient air is too humid, the moisture does
not evaporate from your body quickly in its effort to reach equilibrium, as
the air is already saturated. Your body doesn’t cool very effectively.
The same thing happens when you make snow. Water vapor gives off heat as it
evaporates, accelerating the freezing process. Snowmakers are more interested
in the "wet-bulb" temperature, which is a mathematical function of
the dry bulb temperature and the level of humidity. Warmer air holds more moisture
than cooler air, all other things equal, and the temperature at which 100% humidity
is reached is called the "dewpoint". At the dewpoint, the wet bulb
temperature and the dry bulb temperature are identical. On a very dry day, however,
the wet bulb temperature may be below freezing when the dry bulb temperature
is above freezing, and you can actually make snow! Likewise, if the temperature
is near the dewpoint, although both are a bit below freezing, the water droplets
will not freeze quickly enough to create snow.
Additional cooling is provided by the energy released as the compressed air
returns to ambient pressure. Think back to high school physics, and you’ll recall
that temperature is directly related to pressure; all other things being equal,
a substance will increase in temperature as pressure increases. The release
of the compressed air through the snowgun nozzle transforms some of that heat
energy into kinetic energy, which is used to propel the water vapor skyward.
The rapid release of heat energy quickly cools the water vapor as well.
An alternative to the traditional water/compressed air mix is offered by such
manufacturers as Hedco and Lenko.
Using a snow cannon, a large amount of water is atomized through many tiny nozzles
surrounding a giant fan blade. This fan propels the moisture into the air, where
it condenses and freezes to form snow crystals.
are both distinct advantages, and disadvantages to this technology. Snow cannons
generate a tremendously greater amount of snow per hour than a traditional air/water
gun. For example the Hedco Super "D", pictured at right mounted on
a snowcat, can pump out a foot of snow over 2.1 acres in 12 hours, at 10º F
and 60% relative humidity using 400 gallons of water per minute. They are also
much quieter to operate. There’s also no need for costly air compressors and
a dual pipeline to service the hydrants – instead, the resort runs a relatively
inexpensive electrical power line alongside the water pipes to provide the energy
necessary to run the fan.
The snow created by snow cannons, however, is much wetter and denser than that
created by traditional snow guns. They’re costly to purchase, running roughly
$10,000 apiece not including any kind of transportation device. They’re also
far less mobile, making frequent movement to create an even snow distribution
problematic, at best. You’ll often find resorts with snow cannons creating huge
snowmaking "whales," then using a groomer to spread out the product
across the trail (or as I saw done at Stoneham and Mont Sutton, both in Québec,
even a backhoe!). Mont Tremblant is installing a Flowtronex
airless system on its expansion this summer.
THEY’RE NOT MAKING SNOW, THEY’RE MAKING A MESS!!
our nature as snow connoisseurs, you would expect that snowmakers would always
try to create a dry product. That, however, is not always the case. Wet snow
is more durable, and covers terrain features more effectively. For that reason,
especially early in the season, snowmakers endeavor to create an effective base
with heavy, wet man-made snow. Many resorts, bowing to cost-effectiveness, will
cover a run once or twice a season with dense man-made snow, then merely groom
it as required throughout the year. Although this is an effective technique
in high-traffic areas, the surface will quickly degenerate to a hard, icy consistency
by mid-day if skier volume is even moderate.
Even at ski areas where money in the snowmaking budget flows more liberally,
the base will be comprised of heavy, wet snow. Often it is so wet that resorts
will leave the trail closed for a day or two, allowing the water to drain from
the snowpack before grooming it out. Subsequent lighter, drier layers will be
added to create a pleasant skiing surface.
resorts have replaced the jacket test with sophisticated computerized distribution
systems, allowing a control operator in a single room to control the compressors,
the water pumps, and even the valves and air/water mix at individual hydrants!
Remote weather sensors scattered about the mountain radio data to the operator,
who uses a computer program to determine the ideal air/water mix for the given
It’s a simple premise: the higher you mount the gun, the longer the moisture
has to freeze before hitting the surface. You can therefore use a higher water/air
ratio, putting out more snow volume and reducing the compressed air expense.
You can also make snow in marginal conditions that would preclude operation
with a conventional gun or cannon. Snow Economics
of Natick, Massachusetts is one of the United States’ leading manufacturers
and distributors of tower guns.
guns are expensive, especially because they’re not portable. For that reason,
they first appeared only in high traffic areas, such as those surrounding lift
drives. They have since proliferated to the point that they cover entire trails.
As snowmaking experts Orville and Izzy Slutzky of Hunter Mountain, New York
have shown, you can even mount a snow cannon atop a tower.
OH, THE EXPENSE OF IT ALL!
Labor is the single most expensive portion of a ski area’s operating budget.
Running a close second, however, is electricity. While some diesel air compressors
are in service, most used for snowmaking are powered by electricity. Ski areas
have negotiated special contracts with their local power authorities, enabling
them to create snow at a reduced cost when demand on the power grid is at a
low point. To purchase them, installed compressors cost approximately $250,000
apiece. These compressors are fairly sophisticated pieces of equipment. Most
snowmaking systems generate pressures of 80-100 psi, although some can operate
at pressures as high as 150 psi. Don’t forget that temperature/pressure relationship
– the greater the pressure, the more heat is transferred to kinetic energy as
the air is released through the snow gun nozzle.
people assume that water is the most expensive component of snowmaking, due
to the sheer quantities of water involved. For example, Sunday River, Maine’s
snowmaking system coverts 9,000 gallons of water per minute into snow. That’s
enough to make 3100 cubic feet of snow, covering a football field, including
the end zones, with 3.5 feet of snow in one hour!
Most modern snowmaking systems use a reservoir to store their water supply
on site, and these are designed to replenish themselves. The natural drainage
of the ski resort’s terrain returns this to the watershed, even during the winter
when runoff melts under snowpack. If designed properly, much of this runoff
finds its way right back into the snowmaking pond.