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Episode 07

Why Do Ski Resorts Store Snow Under Sawdust?

Resorts make snow in deep winter, when it's cheap, and bury it under 30 to 40 cm of wet sawdust. About three-quarters of it survives the summer. Here's why.

1 November 20267 min readVideo 7:25

Ski resorts keep last winter's snow because snow cannons need cold nights that late October may not bring, and deep winter makes snow far more cheaply. So they make it in winter, pile it up and bury it under 30 to 40 cm of wet sawdust, which soaks up the sun's heat and cools as its water evaporates. In a 2008 test in Davos, about three-quarters of the snow survived the summer.

Watch the episode: This Ski Track Is Made of Last Winter's Snow 7:25

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Which ski tracks run on last winter's snow?

Finland's domestic ski season opens at the start of November in Vuokatti, on its stored-snow track. In 2026 that was 31 October to 1 November. Vuokatti stores tens of thousands of cubic metres of snow from the previous winter and opens a track made of it around mid-October. The track is about 1.5 km long when it opens and grows to 9 to 10 km.

Davos, in Switzerland, keeps a 20,000 cubic metre pile under sawdust that becomes a 4 km cross-country trail, opened in 2026 on Friday 30 October. The new season opens on last season's leftovers.

Levi, in Finland, has hosted the alpine World Cup since 2004. Its races were cancelled 3 times for poor snow, in 2007, 2011 and 2015, each time a whole weekend of them. In spring 2016 it built its first storage piles on its race slope.

It's called snowfarming. Snow is piled late in winter, covered, stored over summer and spread at the start of the next season, so a track that opens in mid to late October is made of snow about 8 months old.

Why not just make snow in October?

Resorts already own snow cannons, but cannons need the weather to agree. Snowmaking needs about minus 2°C or colder, ideally a wet-bulb temperature of about minus 3°C or lower, and the damper the air, the colder it has to be. On a mild, damp night, the number of cannons makes no difference.

Davos tourism's head of technical services put it plainly in 2008: snow cannons would be cheaper, but the end of October or the start of November may not be cold enough to rely on them. Races don't wait for the forecast either. The 2026/27 cross-country World Cup is set to open in Ruka, Finland, on 27 to 29 November 2026, a date fixed long in advance.

There is a second reason, and it's money. Levi's 300+ snow guns make its stored snow at around minus 10°C or colder, in January and February, when it is most energy-efficient. At that temperature, Levi says, a gun makes about eight times as much snow as in marginal conditions near 0°C. Making snow in cold, dry winter air takes about a third of the energy per cubic metre that autumn production would. So you make it when it's cheap, and keep it.

Fleece or sawdust: what keeps snow through a summer?

What I really wanted to know was how a pile of snow survives a summer. Levi's pile, the Glacier, is about 650 m long and 50 m wide.

In 2008, researchers in Davos ran a test at about 1,500 m. They piled up 2,500 cubic metres of snow and covered half with fleece, as on glaciers, and the other half with 30 to 40 cm of sawdust. The project leader, Hansueli Rhyner, had a simple rule for packing it: the denser, the better.

By autumn, about a fifth of the snow under the fleece was left. Under the sawdust, about three-quarters. The 900 cubic metres left over made a cross-country trail 500 m long: half a kilometre of skiing for a whole summer of storage.

It has got better since:

Pile	Snow kept over summer
Davos test, 2008, under fleece	about a fifth
Davos test, 2008, under sawdust	about three-quarters
Davos study pile, summer 2015	74%
Martell, Italy, summer 2015	63%
Davos Flüela valley today (about 20,000 m³)	about 80%
Levi under foam covers	up to 90%

The 2015 figures come from a study in The Cryosphere. Davos now loses only about 20% a year. Other operators, in an SLF survey, reported losing 13 to 50%, about 28% on average. And not everything that goes missing has melted: about a third of a Davos pile's lost volume was the snow settling under its own weight.

France does it too. Le Grand-Bornand gathered snow after its 2024 biathlon World Cup race and covered it with sawdust for the next December's race; its biathlon stadium, at 930 m, holds 2 piles of 14,000 cubic metres each. Levi went another way: around 400 insulating mats, each 70 mm thick, 4 m wide and 18 m long. Those covers cut its summer loss from around 30% to as low as 10%.

Why does sawdust work so well?

Fleece works on glaciers, high up. Davos, at about 1,500 m, is on average 5 to 8 degrees warmer than glacier level, so the snow needs real insulation, not just shade.

I expected the trick to be keeping warm air out. Mostly, it's the sun: sunlight was the main source of energy reaching the piles. The sawdust layer stores the day's heat without passing it to the snow, then gives it off at night, mainly by radiating it to the sky. Simulations show it needs to be at least 30 to 40 cm thick. With only 20 cm, the insulating and cooling effects greatly diminished.

It also works better wet. In the study, rain alone kept the sawdust wet all summer, and as that water evaporated it cooled the snow underneath. The pile sweats so the snow doesn't have to. Put together, only 9% of the sun's energy went into melting the snow under the sawdust. Uncovered, the snow would have received 12 times as much.

This is an old trick. In the 1800s ice trade, workers stacked ice blocks with sawdust or salt hay between the layers. One merchant, Frederic Tudor, born in Boston in 1783, became known as "The Ice King of the World". In 1833 his ship the Tuscany carried 180 tons of New England ice about 26,000 km from Boston to Calcutta, with the gaps between the blocks filled with sawdust and wood shavings. How much arrived is disputed: the captain listed 100 tons, just over half, while Tudor's diary says about two-thirds. Nearly two centuries later, a pile in Davos keeps about 4 in 5 cubic metres without leaving the valley.

Is snow farming worth it?

The piles keep growing. In 2023 Levi held a record 130,000 cubic metres, plus 50,000 set aside for its World Cup slope and 20,000 for its stored-snow track. Stored snow has stretched Levi's season from October to mid-May. Before the 2014 Winter Olympics, Sochi stored about 710,000 cubic metres, according to the organizing committee, so the Games could run in any weather.

Spreading the snow again in autumn is the expensive part. At Snow Farming Davos in 2016 it was about two-thirds of the running cost. About half of operators consider it profitable, two-thirds plan to continue, 27% plan to store more and only 5% plan to stop. Their main reasons are a minimum snow sport offer, a punctual season start, and making up for shorter snowmaking periods in autumn. Davos counts another saving: its trail spares national cross-country teams several dozen flights a year to the Scandinavian winter.

It can still go wrong. In 2022, with 19°C forecast, Davos pushed its trail's opening back from 29 October to 5 November at the earliest. Laid out in that warmth, the organisers said, the snow would have suffered badly. The long view is harder still: the Alps may lose as much as 70% of their snow cover by the end of the century if warming continues unchecked. Among operators who don't store snow yet, about half are considering it, and 15% definitely plan to start.

Look at the edges of the picture

At the next early-season ski race, look past the track. If the trees are bare, the ground is brown and only the course is white, that snow is probably older than the season it's raced in.

What's the earliest in autumn you've ever seen snow where you live? Or have you never seen it at all?

Sources

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