The people in charge of making snow for the Winter Olympics in Russia caught a break over the past two months, when for two periods of about a week each temperatures dropped enough to make good snow, and lots of it.
Over all, their snowmaking machines made enough to cover about 500 football fields to a depth of two feet. Together with some natural snow, that should ensure that the skiing and snowboarding events at the Sochi Games, which open Friday, take place on glistening white pistes, even if rain and warmer temperatures arrive.
“Our goal was to lay down 150 to 175 percent of what was needed,” said Jon Wax, a snowmaker from Wenatchee, Wash., who spent December and January working at Rosa Khutor, the Alpine venue for the Games.
Whether in Russia for Olympic athletes or New England for winter vacationers, snowmakers work hard to produce the solid base and dusty powder that can supplement, or in some cases supplant, nature and make for quality skiing. If there is an art to getting good snow from a machine, it is based on a thorough understanding of the science, especially the role of temperature and humidity in the process.
Machines make snow the same way nature does, by freezing water droplets. But they do it a few feet above the ground, rather than in the much colder conditions high in the atmosphere. Snowmaking machines employ a few thermodynamic tricks to help, but at times there is a limit to what physics can do.
Snowmakers pay special attention to wet bulb temperatures, which take humidity into account along with the actual air temperature. At Rosa Khutor, which is only 25 miles from Sochi, the host city on the Black Sea where conditions are subtropical, wet bulb readings can often be too high to make snow. Or, if snow can be made, it may be little more than water droplets with a bit of ice around them.
“I’ve been making snow for 17 years, and I’ve very rarely made snow at 28 degrees wet bulb,” Mr. Wax said. Such a reading — which, if the humidity is 50 percent, means the air temperature is 34 degrees — is considered poor for snowmaking. But except for those two weeklong intervals, when wet bulb readings dropped to around 21 or 22 degrees, he said, he made snow in marginal conditions.
Rosa Khutor may be particularly difficult, but no ski resort is immune to the problem of poor conditions — even those in New England, where the air can be so cold that skiers are warned about frostbite.
Early in the season, the best snowmakers might hope for is very wet snow, said Dave Moulton, director of mountain operations at Mount Snow in West Dover, Vt. “Sometimes you don’t have a choice,” he said. “You just want to make the ground turn white.”
Even very wet snow can serve a purpose. Once on the ground, it will freeze fully and harden, providing a decent base for the better snow to come.
In the dead of winter, very wet snow is seldom the problem. One evening last week, Mr. Moulton was turning on snow machines on a wide trail called Snowdance, opening valves on each barrel-like machine to send up to 107 gallons of water a minute through a ring of nozzles. (With more than 200 such machines, Mount Snow, like all snowmaking resorts, uses a lot of water and power.)
A powerful fan on the back of each machine blew the fine droplets out over the slope where, with the temperature near zero, they froze and wafted down as a crystalline mist, about as close to dry powder as a machine can make.
Even in very cold air, droplets need help to freeze. Water can be supercooled, to about minus 50 degrees Fahrenheit, and remain liquid if there is nothing for the molecules to crystallize around.max volume
High in the atmosphere, the crystallization is aided by dust particles or other impurities, which serve as a seed or nucleus. In many snow machines, seeds are created by the machine itself, through one or more “nucleation” nozzles in which water and compressed air mix.
Coming out of the nucleation nozzle, the air expands, and in doing so cools so rapidly that the accompanying water freezes instantaneously into tiny ice crystals. They seed the larger droplets from the main ring of nozzles. Once they are blown out over the slope, the seeded droplets lose heat to the surrounding air as some of the water molecules evaporate. But if the air is humid, less evaporation, and thus less cooling, is possible. So even on a very cold day, a droplet may not freeze entirely during the few seconds it takes to fall to the ground — what snowmakers call hang time. “We’re basically making eggs,” Mr. Moulton said — icy shells around still-liquid centers. Snowmakers often let machine-made snow sit for a half day or longer to cure, or freeze through, before sending a trail groomer over it. On the other hand, in extremely dry air, droplets can freeze at least partly even if the air temperature is slightly above freezing, because more of the water molecules evaporate. “The colder the air, the drier the air, the more freezing capability we have,” said Joe VanderKelen, president of Snow Machines Inc., a company in Midland, Mich., that makes the machines used at Mount Snow and at Sochi.Still, well-frozen machine-made snow does not look much like what nature makes. Because it forms so quickly, it resembles tiny pellets rather than the elaborate flakes that can grow for hours as they float down from high in the sky.
Snowmakers learn to change the quality of snow — generally wetter for base layers, drier for a top, skiable coat — by adjusting the amount of water coming through the main nozzles. For air of a given temperature and humidity, adding more water will mean that each droplet cools less, making the resulting snow wetter.
For the Rosa Khutor snowmakers, adjusting the quality was seldom an issue; they made whatever snow they could. “Desperate times call for desperate measures,” Mr. Wax said. In marginal conditions, “it’s really hard to control the quality,” he added. “It is what it is.”
So when the temperatures dropped during those two periods, the snowmakers went all out. Rosa Khutor, a new resort, had installed a huge snowmaking system for the Olympics, with more than 400 machines and many other features, like equipment to cool the water to near-freezing before it reached the machines. At times, snowmakers also added inactive bacterial proteins to the water to provide additional seeding capability.
“Because of that system, a lot of snow could be made in a short time,” Mr. Wax said.
In all, the machines converted about 230 million gallons of water to snow, or about 10 times the amount used in a full season at Mission Ridge, the ski area where Mr. Wax is the head snowmaker.
In preparation for the Games, the organizers hired Mikko Martikainen, a Finnish consultant, to plan for adequate snow. Among other things, he recommended stockpiling snow last season; about 650,000 cubic yards of it were stored in huge piles under insulated blankets on north-facing slopes in the area, ready to be trucked to the Olympic courses this winter if needed. But in an email, Mr. Martikainen said that because of the success accumulating natural and machine-made snow this year, most of the stockpiled snow would not be used.
At Mount Snow in Vermont, there is never talk of stockpiling snow from one year to the next. After the early part of the season, conditions are usually cold and dry enough to make good snow, with a medium amount of moisture — what most snowmakers call “production” snow.
But good, cold snowmaking weather can cause other problems. Freezing of the pipes that supply water to the machines, for example, becomes a near-constant concern. Mr. Moulton’s lead snowmaker, Randy Barrows, has enough experience to quickly calculate how to balance water pressure and the number of machines in operation to keep water flowing fast enough in the pipes so it will not freeze.
Still, in extreme cold, when the machines are running at full tilt, sometimes the nucleating nozzles can freeze. When that happens, the droplets from the main nozzles no longer have seeds to help them freeze, so they come out of the machine as rain, which then freezes as it hits the ground, forming a solid layer of glare ice.
Mr. Moulton said it was easy to tell if nucleating nozzles had frozen: If the mist coming from a machine remains a liquid, it catches the light differently.
“We always say, if you see a rainbow, you’re in trouble,” he said.
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