Snow is an essential element of the ski experience. But what exactly is it? Snow forms when water vapor freezes directly into ice crystals, usually around a tiny speck of dust called a nucleus. The resulting snowflakes are incredibly complex. They only grow as quickly as the conditions allow, so they take shape in their own unique designs.

The Weather

The most obvious and crucial factor that determines ski conditions is weather. Ski resorts can only operate in areas with sufficient snowfall, and climate change is making this less likely. A recent study found that in Austria, for example, the ski season may be shortened by one month due to climate change, with negative impacts on local economies and the enjoyment of skiing as a sport.

In the simplest terms, snow is ice formed from water vapor that freezes and falls from clouds. However, snow is more than just frozen rain (which is sleet) or melted water, because of the complex microstructure of the crystals that form it. This has a significant impact on the thermal, mechanical and electromagnetic properties of the snow. It also influences its durability and surface characteristics, and the microstructure can even affect the speed at which it falls.

Various shapes can be seen on a snowflake, but every single one starts as a microscopic crystal that is composed of six sides with different lengths. The shape of a snowflake can be influenced by the temperature and humidity it is exposed to. Scientists have found that these six sides can form into different shapes, including stars, plates, columns and dendrites. These different shapes can help the snow to absorb, reflect or transmit solar energy.

These crystals form when water vapor freezes in the air, and a crystal’s shape depends on factors like pollution, wind speed, humidity and altitude. It is also affected by the temperature and light around it, which explains why no two snowflakes are alike.

As the world gets warmer, scientists predict that more than half of Europe’s ski resorts will be at risk for low snow cover if temperatures rise by 2°C. Some resorts can extend their seasons with artificial snow, but this comes at a cost, using large amounts of water and electricity and creating greenhouse gases.

The Base

Snow doesn’t just come from nature. Ski resorts can also make it themselves, using machines that shoot droplets of water into the air that freeze and fall as snow. It’s important for the snowmaking process that the temperature is just right. Too warm and the water will evaporate too quickly, leaving slushy snow. Too cold and the water can freeze in the pipes, damaging them. The ideal temperature is between -5 and -25 degrees Celsius.

Snow isn’t just a white powder; it’s a complex substance with properties that are measured and studied by scientists. Some of these properties include snow density, surface features, and how the snow is shaped and moved around. Snow density measures the amount of mass per volume of a known volume of snow, usually expressed in kilograms per cubic meter. Surface features describe the general appearance of the snow surface, including deposition and redistribution by wind, melting and refreezing, sublimation and evaporation, and erosion. Snow hardness is the resistance to penetration by an object, typically measured using a hand or fist (very soft through medium), a pencil or knife above the hardness boundary of ice (hard), and a screwdriver above that (ice).

Scientists have studied the way snowflakes form, too. They’ve found that they often form hexagonal shapes, although no two snowflakes are exactly alike. Ornate snowflakes, with many feathery branches, are most likely to be formed under conditions of rapid growth, says University at Buffalo chemistry professor Jason Benedict.

But even if it’s the perfect conditions, skiing can still be a bit of a gamble. A skier can hit a tree or rock and get stuck, which could be dangerous for them and other skiers. And the snowplows that clear the slopes can create huge piles of snow that are difficult to traverse on foot or by car, let alone with skis on.

But the most important thing that affects skiing conditions is how much new snow there is. Skiers and snowboarders need fresh powder to slide on the slopes, so researchers have looked at how resorts report snowfall — and why it might be that some are over-reporting. Zinman and Zitzewitz found that factors like terrain, competition with other resorts, money back guarantees, and local population sizes all affect how much a ski resort reports getting.

The Pistes

Ski runs are known as pistes in most countries, and they are usually colour coded (green for beginners, blue for intermediates and black for expert skiers). They are regularly checked, groomed and protected against avalanches.

The condition of the pistes is also dependent on the location of the slope, weather conditions and time of year. Lower, tree lined runs tend to hold onto their snow better than higher slopes which are more exposed to the sun. As well as this, the lower slopes need less snow to be skiable, especially towards the end of the season when the sun is warming up the pistes.

A good quality piste will be skiable on all levels – from powder through to hardpack. However, even a well-groomed piste can become unskiable if the weather suddenly changes (e.g. when the wind shifts huge amounts of snow in a very short space of time). For this reason, some pistes are closed for safety reasons if conditions are too dangerous.

Resorts are also often required to rely on snow cannons when there is not enough natural snow. These work by shooting pressurised air and cool water at high speed, which freezes to form snow particles that fall on the snow below. They are particularly useful in the early part of the season when there isn’t a lot of natural snow already present on the mountain.

Although not ideal, this is a necessary step to ensure that the slopes are open and safe for skiers to use. Besides this, it also helps to limit the number of people skiing on the slopes which can cause excessive wear and tear. This can affect the quality of the snow too as it becomes icy and compacted. However, these machines are expensive to operate and require a significant amount of energy to run, so they are only ever used as a last resort.

The Skiers

Snow and skiing are not only a beloved winter pastime for many, they’re also a critical component of small economies in colder regions. However, climate change is making it harder for Lakes resort Mammoth to function at their best. To ensure a good season, many resorts turn to snowmaking, which requires substantial amounts of electricity and water. This isn’t a foolproof solution. For example, the process can be affected by conditions such as wind and temperature, which impact the speed at which water droplets are sprayed.

While it’s not an easy job, these systems are critical to the success of many ski resorts and to the safety of skiers. In fact, the risk of injury for winter sports participants peaks when speed exceeds safe limits. In order to avoid this, many skiers have to learn how to manage their speed on slopes. Past research has shown that actual speeds of signposted groomed slope skiers and their skill to accurately estimate them are heavily influenced by diverse individual demographic and behavioural factors [1,3].

The authors of this study wanted to expand upon this understanding by investigating how environmental factors affect adult more-skilled skiers’ speed and their ability to estimate it. To this end, they compared five environmental factors: visibility (good/moderate/poor), sky cover (sunny/overcast/cloudy), snow quality (grippy/icy spots/wet), and wind (calm/moderate/strong). The researchers found that the most influential factor was snow quality, followed by visibility and wind. In addition to this, they discovered that the more skilled a skier is, the less likely they are to make speed-related mistakes.