Mountain weather: What clouds reveal

10/04/2024 - SnowTrex

Every winter sports enthusiast knows what it’s like: getting up in the morning, going to the window, carefully pulling the curtains aside and thinking: “I hope the skiing weather is good”. And if it’s not exactly glorious sunshine, the view of the sky can sometimes be puzzling. Because when it’s cloudy, the question arises: How are these clouds to be read? SnowTrex explains exactly what the different types of clouds reveal about the current mountain weather and what they mean for skiing.

Clouds are simply part of the weather in the Alps, even in winter

Cloud typeHeightWeather situation
layered clouds0,0 to 5 kmDrizzle
Rain clouds0,1 to 6 kmRain/snow
Cluster clouds0,5 to 2,5 kmCloudey
Storm clouds0,5 to 11 kmThunderstorm
Fleecy clouds2,5 to 12 kmRain/snow
Lenticular clouds3 to 6 kmalmost clear
Mammatus clouds5 to 10 kmRain/thunderstorm
Veil clouds6 to 10 kmOncoming rain
Feather clouds6 to 12 kmClear/sunny

What are clouds?

Clouds are formed when water droplets adhere to small particles in cold layers of air. This makes them visible in the sky as condensed water vapour. As clouds can be at different heights, they can be roughly divided into four categories: low clouds (0 to 3 km above the ground), medium-high clouds (2 to 7 km), high clouds (7 to 12 km) and clouds that extend vertically over several of these “storeys”. Clouds, which are not always rain clouds, always take on the ambient temperature, making them very cold at high altitudes, unlike at ground level.

They can also be categorised according to their appearance: Cumulus clouds, for example, popularly known as fleecy clouds, are formed by rising air. Stratus clouds, also known as stratus clouds, are formed when warm air pushes over cold air. But what do the different types of clouds actually mean? And what should winter sports enthusiasts be prepared for when they see veil clouds in the sky?

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Weather with stratus clouds

Layered clouds (stratus) are also categorised into different “storeys”, as they can form directly above the ground or up to 5 km above the ground. When mid-level stratus clouds – known as “altostratus” – form, the sky initially clouds over slowly but steadily. For winter sports enthusiasts, this means that visibility on the piste becomes increasingly poor and the weather conditions soon change with precipitation.

Weather with rain clouds

A rain cloud, which turns into a snow cloud at higher, colder altitudes, also known as a nimbostratus, also forms in several levels in the sky between 100 metres and 6 kilometres high. This cloud form barely lets the sun through, which is why its underside can usually appear from a light grey to almost black. If this type of cloud appears, it means, as the name suggests, that it will soon rain or even snow in the mountains! The precipitation can make poor visibility on the slopes dangerous for skiers. Depending on the amount of snow, the probability of avalanches in the ski area increases, especially away from the pistes.

Rain clouds can ensure abundant snowfall and the best deep snow conditions in the mountains in winter. However, freeriders must always be aware of the risk of avalanches!

Weather with cumulus clouds

Cluster clouds or cumulus clouds, also known as stratocumuli, can easily be confused with cumulus clouds, which is a challenge for mountain enthusiasts because: While cumulus clouds usually promise a lot of sunshine, cumulus clouds at an altitude of 500 m to 2.5 km primarily only herald an improvement in the weather. The clouds mainly form in the mountains because the wind there blows moist air masses quickly over the peaks. This cools the air and mainly clusters of clouds form. Like many other clouds, these often “get stuck” in mountain ranges such as the Alps, as the mountains form a natural barrier and the clouds have to slowly rise up their flanks to the summits:

Forming cumulonimbus (timelapse)

Weather with thunderclouds

When small fleecy clouds grow rapidly in height, this is a sign of an imminent change in the weather. This is because the initial fleecy clouds quickly develop into thunderclouds, which are among the most dangerous clouds of all and are also known as cumulonimbus or ambos in technical jargon. They pass through several “storeys” between 500 m and 11 km high and herald thunder and lightning, which can be dangerous for skiers outdoors on the piste.

Weather with fleecy clouds

Cumulus clouds, commonly known as fleecy clouds, usually form in stable high-pressure weather at an altitude of 2.5 to 12 kilometres. And they make every winter sports enthusiast’s heart beat faster, as they promise a sunny day without any changes in the weather. However, caution is advised when the fleecy clouds rise quickly. This can be a sign of approaching rain or snow in the mountains.

Clouds in the mountains can create a spectacular atmosphere in the sky

Weather with foehn clouds

Like the fleecy cloud, the foehn cloud belongs to the cumulus cloud category. They are also referred to by weather experts as “altocumulus lenticularis” and occur at an altitude of 3 to 6 kilometres, where they form the round shape of a UFO. These clouds form when the foehn wind blows on the mountain ridges, precipitation falls in the stagnant areas of the wind and warm, sunny Alpine weather prevails on the leeward side of the mountain – i.e. the side facing away from the wind. Meaning: If the ski area is on the leeward side, winter sports enthusiasts and mountain lovers are lucky with the weather. At the summits, however, strong gusts of wind can also occur here, which then pose a danger to skiers.

Weather with mammatus clouds

Mammatus clouds are unusual, bag-like cloud formations that form on the underside of thunderclouds. There is usually strong turbulence in their vicinity. In addition, the formation of mammatus clouds heralds possible thunderstorms, which means an increased risk of a sudden change in weather conditions for skiers in the mountains. This type of cloud occurs at an altitude of 5 to 10 kilometres.

Weather with veil clouds

Veil clouds, also known as cirrostratus, stretch like translucent veils across the entire sky at an altitude of 6 to 10 kilometres. When skiers and snowboarders see this type of cloud, they can usually assume that it will rain or snow around 36 hours later.

Veil clouds can form at an altitude of up to 10 kilometres and usually herald a change in the weather over the next few days

Weather with feather clouds

Feather clouds, also known as cirrus clouds or ice clouds, are the highest of all cloud types at a height of 6 to 12 kilometres in the sky. In the singular, weather experts speak of cirrus, which means “tuft of hair”. This describes their appearance quite well, as they are fine, scattered, thread-like clouds whose edges are mostly frayed. The contrails that aeroplanes leave in the sky every day also belong to this category. Cirrus clouds usually herald the arrival of a warm or cold front in sunny weather.

What will the weather be like in the Alps next week? The snow weather forecast for each destination can be viewed at SnowTrex:

FAQ about clouds and mountain weather

What do cumulus clouds mean for skiing weather?

Cumulus clouds, often also called fleecy clouds, form at an altitude of 2.5 to 12 kilometres and are usually a sign of stable high-pressure weather that promises sunny conditions for winter sports enthusiasts without weather changes.

How do foehn clouds affect the weather in the ski area?

Foehn clouds, also known as “Altocumulus lenticularis”, occur at an altitude of 3 to 6 kilometres and form in foehn winds. On the side of the mountain facing away from the wind, they often herald sunny weather. At the summits, however, they can also lead to strong gusts of wind that can be dangerous for skiers. Rapidly rising foehn clouds, on the other hand, are often a sign of imminent rain or snowfall.

What weather changes should skiers be prepared for in the event of thunderclouds?

The rapid growth of small fleecy clouds into thunderclouds, also known as cumulonimbus, indicates an imminent change in the weather. These clouds, which are between 500 m and 11 km high, signal lightning, thunder and possible dangers for skiers on the slopes.

How do the weather conditions change for skiing when stratus clouds form?

Layered clouds (stratus), which can form at various altitudes up to 5 km, slowly cloud the sky and reduce visibility on the piste. Medium-high stratus clouds, known as altostratus, often herald impending precipitation.

What does the appearance of mammatus clouds mean for winter sports enthusiasts?

Mammatus clouds are unusual, baggy cloud formations that occur at an altitude of 5 to 10 kilometres and herald strong turbulence and possible storms. Their appearance means an increased risk of sudden weather changes for skiers in the mountains.

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