The western parts of the European Alps has seen a huge “snow dump” the past day – and more is yet to come. This has caused a red alert in the Wallis / Valais region in the south of Switzerland.
Some areas have seen over 70cm of fresh snow and there is more to come: another 15-30 cm is expected according to MeteoSuisse. However, the SLF expects a considerable larger amount of snow.
This is what the SLF (Snow & Avalanche center) states:
“With widespread heavy snowfalls and stormy westerly winds, further extensive accumulations of snowdrift will form in the west and north. The connection of the new and snowdrift layers to the old snow surface is generally quite favourable. Only on northern slopes at higher altitudes, however, was the snow surface partly angular and formed a weak base there.
In the inner-Alpine areas of Graubünden and partly also in Valais, the snowpack structure on northern slopes is still weak. Up to around 2000 m, the snow cover gets wet with the rain and loses stability. Wet snow avalanches are to be expected.”
The snow from yesterday (Wednesday April 6 to Thursday, April 7) fell above 1800 m as snow, sinking slightly to 1600m during the night. The amounts of fresh snow were up to 100cm in the west.
Avalanche risk this time of year
With the beginning of spring, the sun gets increasingly stronger. This causes changes in the surface area of the snow pack. But also the rising temperature itself is causing instabilities to the snow pack. However, April is still a winter-month high up in the mountains. The largest snow depth is usually measured mid-March to Mid-April, depending on the altitude and latitude.
Spring is the usual time for “wet avalanches”: an increasing weakening of the snow cover due to the ingress of water, either from melt or rain. As solar radiation is the main cause of the melt, the spread depends primarily on exposure. Air temperature and humidity determine distribution by altitude.
When rain is the cause of water ingress, all exposures are affected (regardless of its exposure to the direct radiation).
An addition to this risk is when the snow-pack is close to the freezing level: water does not re-freeze again in the snow pack and large areas can become unstable quite sudden.
With current conditions, the risk is obvious: the freezing level is at a high altitude (near 2000m) and the rain fraction is substantial over a large part of the mountains.
During the weekend, the risk subsides as the wind gets calmer and the precipitation is moving out.