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Reading tip | SLF season report for winter 2016/17

The Swiss Avalanche Warning Service looks back on the past season

by SLF 11/27/2017
The SLF's seasonal report on the 2016/17 avalanche winter in Switzerland is also available online. The report contains detailed information on the weather, snow cover and avalanche risk.

Here is the online view, here the pdf. The most important key data is summarized here in the article.

Little snow at the end of the year and little danger of avalanches

The winter got off to a promising start in mid-November with heavy snowfall. However, the snow then melted again below around 2000 m during a foehn phase lasting several days. December was then drier and less snowy than at any time since records began. By the end of the year, there was usually not enough snow for touring and off-piste skiing. Many winter sports resorts experienced a green Christmas for the second time in a row. The widespread thin snow cover varied greatly in structure on a small scale and was often influenced by the wind. There were often several crusts, sometimes it was completely transformed and loose.

Critical avalanche situations for snow sports enthusiasts with fresh snow and weak old snow

In January, repeated snowfall and foehn storms led to critical avalanche situations in the west and north, then from February onwards in the east and south. The danger came mainly from layers of new and drifting snow as well as weak old snow at the base of the snowpack. In the north and west, the weak foundation was soon well covered and could no longer be triggered by people. Especially in southern Upper Valais, northern Ticino, the inner alpine areas of Graubünden, the Engadine and the southern valleys of Graubünden, the weak base layers of the snowpack remained a danger until March due to the thin cover. This was the only weak layer that remained in the snowpack for a long time this winter.

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Exceptional avalanche activity at the beginning of March with many large, spontaneous avalanches

At the beginning of March, several large snowfalls with a fluctuating snow line in combination with the weak old snow cover led to very high avalanche activity. Many large avalanches and some very large avalanches were triggered spontaneously, causing damage to roads, forests and buildings.

Increasingly favorable spring situation, then wintery again

March was very warm and the snow from the beginning of the month quickly melted away again. From mid-March, the avalanche situation was widely favorable. Due to the high avalanche activity at the beginning of March, many slopes were unloaded or already soaked. As a result, relatively few wet snow avalanches occurred in spring. Winter returned again in mid-April, with snowfall down to low altitudes and a worsening of the avalanche situation at high altitudes. As a result, snowpack loss was somewhat delayed until the beginning of May. After that, the snow cover lost mass very quickly with persistently high snow melt rates, even in the high mountains.

    Extremely short winter with little snow

    The extremely late snowfall and early thawing led to an extremely short duration of snow cover at some stations. Last winter was one of the shortest and least snowy winters in Switzerland since measurements began. The almost average snow depths in some valleys at the foot of the Pre-Alps (e.g. Thun, Schwyz or Linth Plain region) are an exception, which were solely due to the snowy January in these regions.

    In the winter of 2016/2017, south, south-west and west-facing locations were somewhat less frequent, especially in the fall (October-November) and in the height of winter (December-February).

    The winter of 2016/2017 (November-April) was significantly warmer than normal, although less warm than the previous winter. The course of the zero degree line in Figure 3 shows the comparison with the average of the 15 previous years. According to MeteoSwiss measurements, Switzerland experienced the sixth warmest winter period (November-April) since measurements began in 1864. This period was only warmer in 2006/07, 2015/16, 2013/14, 1989/90 and 2014/15.

    Over the entire winter, snow depths were clearly below average everywhere in Switzerland, although only slightly so in the west and Valais. The south was more affected by the lack of snow than the north.

    Fewer avalanche victims than the long-term average

    On average, the winter of 2016/2017 was less avalanche-prone than in the previous ten winters (see section "Avalanche bulletins and danger levels", Figure 34). As Figure 6 shows, the main phases of avalanche activity were in mid-January, early February and - particularly pronounced - in the first decade of March (see section "Avalanche activity"). In spring, the activity of wet avalanches was relatively low. This was mainly due to the fact that many slopes had already unloaded in the first half of March and the snowpack was partially soaked after rain above around 2500 m.

    The total number of fatalities up to the end of May 2017 was 7 - all in open terrain - well below the long-term average. For the entire hydrological year, which lasts until September 30, the 20-year average is 23 avalanche fatalities.

    Summer 2017 (June to September 2017): 11 avalanche bulletins, one avalanche fatality

      Increased avalanche danger was a short-term issue every month during the summer and was mainly concentrated in the high mountains. There were 11 summer avalanche bulletins published (on June 4, 5 and 28, July 24 and 26, August 9 and 31, and September 1, 9, 15 and 17). This number of summer bulletins is significantly higher than the average of five avalanche bulletins over the last ten years. There was one fatal avalanche accident in summer 2017. The long-term average for the months of June to September is two fatalities.

      This article has been automatically translated by DeepL with subsequent editing. If you notice any spelling or grammatical errors or if the translation has lost its meaning, please write an e-mail to the editors.

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