SnowFlurry 2 2025/26 | "Under the magnifying glass"

The current snow situation:

On the weekend of 11.01.2026, there was finally snow again in the Alps. Although the snow depths in the Central Alps are still well below average, a much thicker snow cover has already built up in the Western Alps (Fig. 1). However, the fresh snow at the weekend has also led to a tricky avalanche situation. With up to 80 cm of fresh snow in places, an avalanche warning level 4 was issued for Sunday, January 11, 2026, across almost the entire French Alps and along the main Alpine ridge into Tyrol.

Our profiles:

Directly before the last precipitation, on January 7, 2026, we were doing field work on the Madrisahorn above Klosters in Graubünden. At an altitude between 2,500 and 2,700 m, we dug three snow profiles in different exposures to investigate how the snowpack is structured depending on the slope direction and on which base the fresh snow will lie. The profile locations can be seen on the map in Figure 2.

Using these profiles, it is very easy to understand how the snowpack develops differently depending on the exposure and which processes lead to the snowpack being more unstable on north-facing slopes than on other slopes.

First a brief classification: The differences discussed here are general probabilities and tendencies, not absolute statements. Depending on the local conditions and the weather at the specific location, other effects can also dominate, contrary to the general tendency. Furthermore, all sun-dependent phenomena relate to the northern hemisphere. In the southern hemisphere, these phenomena occur in exactly the opposite direction. The position of the sun also influences the extent of the differences between northern and southern slopes. In polar regions or at the height of winter, the differences are therefore more pronounced than near the equator or in late winter.

Wind-driven processes in particular, such as snow drifting, which have a strong influence on snow depth, are extremely dependent on the local topography. This includes the main direction of the valley or pass, small-scale changes in slope inclination or vegetation as well as many other terrain characteristics. General statements can never fully reflect such subtleties; a local assessment always provides more precise information.

Enamel crusts

The first noticeable difference between the three profiles is the different hardness of the individual layers. The hardness of a layer is shown in the snow profile by the gray bars pointing to the left.

In the southwest profile, hard melt crusts make up a large proportion of the total snow depth and reach knife-edge hardness in places. In the east profile, on the other hand, there are significantly fewer melt crusts and they are less hard overall. This tendency is further reinforced in the north-east profile, where only a single melt crust remains. These differences can be explained very well by solar radiation. Melt crusts form on the surface of the snow cover at comparatively high temperatures or through direct sunlight when the snow crystals in the uppermost layers begin to melt.

The resulting liquid water does not immediately flow down through the snow cover, but is initially absorbed by the surrounding layers like a sponge and distributed in their cavities. When the snowpack cools down again overnight or during a colder period, this water freezes in the previously filled cavities, creating denser, harder layers with very strong bonds between the individual crystals. Since southern slopes receive the most direct sunlight and also have higher air temperatures than other exposures, while northern slopes receive the least sunlight, it is not surprising that we can observe this clear gradation in the formation of fusion crusts.

Melt crusts, especially thick and well-developed ones, usually have a stabilizing effect on the snowpack. Due to the strong horizontal connections between the snow crystals, an additional load, for example from fresh snow or winter sports enthusiasts, is distributed over a larger area. As a result, the pressure has less of an effect in depth and the risk of triggering an underlying weak layer is reduced.

Weak layers

We also observe a similar difference in the layer hardnesses in the other layers that do not consist of fusion crusts. While these layers in the southwest profile predominantly have a hardness of one finger, the hardness in the east profile is mostly between four and one finger. In the north-northeast profile, on the other hand, large parts of the snowpack are only about fist-hard, even in deeper layers. These differences can be explained by the transformation processes within the snowpack. As already described in the last SnowFlurry article, temperature differences are the driving force for the formation of angular crystals and thus for the formation of weak layers. It is precisely these temperature differences that are significantly greater on north-facing slopes than on south-facing slopes.

This can be seen very clearly in our profiles: the uppermost layers on the northern slope are as cold as -26 °C, while the lowest temperature measured on the south-western slope was only -16 °C - which, trust us, is still pretty cold for a day of fieldwork. Due to the larger temperature gradients on north-facing slopes, the humidity there moves more efficiently within the snowpack. This allows angular crystals to grow faster and take on larger shapes. This is reflected both in the grain sizes and in the crystal shapes. In the north slope profile, the crystals are larger at almost all depths, and the upward transformation, from small, round crystals to angular shapes and cup crystals, is more advanced than in the other exposures.

Accordingly, these layers are also less hard, as large angular crystals or cup crystals are only loosely bonded together. This is critical for the stability of the snowpack: the looser the snow in a layer, the weaker it is. This increases the risk of slab avalanches, as additional loads such as fresh snow or winter sports enthusiasts can trigger these weak layers at a later date.

These tendencies of different avalanche risks depending on exposure can also be clearly seen in data. In their paper " Characteristics of human-triggered avalanches", J. Schweizer and M. Lütschg show that northern exposures are most frequently affected by fatal avalanches:

"Considering only the avalanches that caused fatalities, the northern aspect is the most frequent one (23%), followed by northeast (18%) and northwest (17%)."

This correlation is also clear in the corresponding Figure 4 on avalanche accidents in Switzerland: there is a clear surplus of accidents in northern exposures, especially compared to southern slopes. Taken together, the three northern sectors account for around 58 % of fatal avalanche accidents in Switzerland. This trend is also confirmed in data sets from other countries and even on other continents (Reuter et al. 2023).

It is therefore not without reason that the avoidance of the three northern sectors is considered a key reduction factor in avalanche risk management. This is reflected, for example, in the Quantitative Reduction Method (QRM), in which exposure is explicitly taken into account as a risk factor (for QRM see e.g.: PowderGuide or Skitourenguru).

Figure 4 also shows that avalanche accidents occur slightly more frequently on east-facing slopes than on west-facing slopes. One possible reason for this is the location of Switzerland, as well as the entire Alps, in a westerly wind zone. Although the wind direction varies greatly depending on the weather conditions, on a long-term average the wind blows more frequently from the west. As a result, western slopes, which are mostly upwind, tend to be blown off, while drift snow accumulations are more frequent on eastern slopes in the lee.

However, this effect is much less pronounced than the fundamental difference between north and south-facing slopes and can vary greatly depending on the valley, exposure and locally dominant wind direction.

Take-Home Messages

• Snow profiles are always local snapshots. The snowpack structure often varies more due to small-scale conditions than general rules and trends would suggest.

• The sun is the most important driver for differences in snowpack structure between the various exposures.

• In the northern sector, the snow tends to be softer and less stable due to lower temperatures and less direct sunlight. This is also reflected in the accident statistics.

• In late winter, when wet snow avalanches become the dominant form of avalanche, the soaking of the snowpack and wet loose snow avalanches, initially on south-facing slopes, must be taken into account.

• The dominant wind direction also plays a role: more avalanche accidents tend to occur on leeward slopes where drift snow accumulates more frequently.

Feel free to write to us in the comments below the article if there is a snow-related topic that is particularly close to your heart that you would like to know more about. You can also ask us questions if something is unclear.