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SLF Winterflash 14/15

Key data for the 2014/15 season

by Christiane Eggert 01/27/2016
The winter of 2014/15 was characterized by an exceptionally snow-poor early winter with correspondingly below-average snow depths. Over the entire winter, snow depths were only just above average above 2200 m and above average on the southern slopes of the Alps. These marked differences in snow depth depending on altitude were caused by above-average temperatures, which repeatedly melted away the snow at medium and low altitudes. With the exception of February, the months of November to March were all too warm, and early winter was record warm in some cases. Despite the excessively warm winter, large parts of the Central Plateau and Jura experienced an average number of snow days thanks to a favorable combination of cold and precipitation. The snow cover build-up was weak in the inner Alps, but also at times on the northern slopes of the Alps, whereas it was much more stable on the southern slopes of the Alps. Compared to the long-term average, last winter was more dangerous. Danger level 3 (considerable) was forecast more than normal, level 2 (moderate) less. Two major avalanche accidents led to an above-average number of avalanche fatalities overall. By April 15, 32 people had died in avalanches.

The winter of 2014/15 was characterized by exceptionally little snow in the early winter and correspondingly below-average snow depths. Over the entire winter, snow depths were only just above average above 2200 m and above average on the southern slopes of the Alps. These marked differences in snow depth depending on altitude were caused by above-average temperatures, which repeatedly melted away the snow at medium and low altitudes. With the exception of February, the months of November to March were all too warm, and early winter was record warm in some cases. Despite the excessively warm winter, large parts of the Central Plateau and Jura experienced an average number of snow days thanks to a favorable combination of cold and precipitation. The snow cover build-up was weak in the inner Alps, but also at times on the northern slopes of the Alps, whereas it was much more stable on the southern slopes of the Alps. Compared to the long-term average, last winter was more dangerous. Danger level 3 (considerable) was forecast more than normal, level 2 (moderate) less. Two major avalanche accidents led to an above-average number of avalanche fatalities overall. By April 15, 32 people had died in avalanches.

The complete, very comprehensive and interestingly prepared SLF season review can also be downloaded as a pdf. Below are the most important key data.

Slab avalanche triggered by people on a western slope at around 2400 m above Karlimatten, Flüelapassstrasse, Davos, GR. The avalanche started in old snow

Typical aspects of winter 2014/15

Weak snow cover in the inner Alps but occasionally also on the northern slopes of the Alps
With very mild temperatures up until Christmas, the winter actually began favorably in terms of avalanche risk. However, as there was very little snow, a weak layer of old snow developed and, similar to the winter of 2013/14, a poor snowpack structure prevailed in the inner Alpine regions of Valais and Graubünden from the turn of the year in winter 2014/15, with the weakest snowpack observed in southern Valais. At times, however, weak layers were also active in the old snow on the northern slopes of the Alps, which is rather untypical for this region and led to several avalanche accidents there. Critical were not only the weak, built-up layers of the early winter at the base, but also snow-covered surface rime in the middle part of the snowpack.

Stable snowpack on the southern Alpine slope
As in the previous winter, the southern Alpine slope also recorded a largely favorably built-up snowpack in the winter of 2014/15. Although the snow depths were not as extreme as in the winter of 2013/14, a stable snow cover was still able to form from the Simplon region to the southern Goms and the central southern slopes of the Alps.

Lots of snow on the Central Plateau and in the Jura
The winter started on 6 November with a lot of fresh snowfall throughout the Swiss Alps, e.g. 56 cm in Göschenen, UR. This remained the biggest snowfall of the winter at most stations. However, these amounts of snow were only short-lived because the massive excess of warmth at the beginning of winter allowed almost no snowfall up to around 2000 meters. Only a cold front at the end of December led to further snowfall, which covered the Central Plateau in particular with large amounts of snow. Due to the lack of early winter snow cover in the Alpine valleys, this briefly led to the paradoxical situation that on December 31, for example, more snow was measured in Zurich and St. Gallen (38 and 56 cm respectively) than in Davos and St. Moritz (32 and 13 cm respectively). However, this snow quickly melted away again with record mild temperatures, before several north-westerly conditions brought snow to the Central Plateau again from mid-January, and this time especially to the Jura. Thanks to a small subsequent cold spell, this snow cover also remained on the Central Plateau for more than 20 days.

Climatological classification

According to MeteoSwiss, the months of November to March were all too warm, with the exception of February, and early winter was record warm in some cases. Last winter's snow depths on the northern side of the Alps were only average above around 2200 meters. This was mainly due to the high temperatures in November and December, which prevented any build-up of snow cover below this altitude at the beginning of winter. On the southern side of the Alps, the snow cover above this altitude was even thicker than average due to the large amounts of precipitation. Below 2000 m, on the other hand, snow depths were clearly below average throughout Switzerland due to the excessively warm winter, even if normal values were briefly reached in some regions. Thanks to the interplay of cold and precipitation at the right time, the number of snow days in the Central Plateau and Jura was even normal in some places despite the warm winter. At the valley altitudes of the large ski resorts (1500 to 1800 m), there was no or very little snow throughout Switzerland during the Christmas period, which was last seen in the winter of 1989/90. Looking at the average snow depths for the whole of December, it is clear that many of these resorts in central and eastern Switzerland have never experienced such a snow-poor December. On the southern side of the Alps and in the Engadine, it was even necessary to wait until mid-January before a continuous snow cover finally prevailed below 1,800 meters. This is in stark contrast to last winter (2013/14), when there was already 150 cm of snow in Bosco Gurin or Maloja at this time.

Avalanche danger

In winter 2014/15, the avalanche danger was assessed as follows (values in brackets: Average of the last 17 years, December to April, see Figure 1): Danger level 1 (low): 20% (17%), danger level 2 (moderate): 39% (47%), hazard level 3 (considerable): 40% (33%), hazard level 4 (major): 1% (2%), hazard level 5 (very major): 0% (0.2%).

The distribution of the forecast hazard levels in winter 2014/15 differed from the long-term average, particularly for hazard levels 2 (moderate) and 3 (considerable): Hazard level 2 (moderate) was forecast less frequently, while hazard level 3 (considerable) was forecast more frequently than the average of the last 17 years. Danger level 4 (major) was forecast in the evening assessment on 6 days. On two days, the risk assessment was changed to risk level 4 (major) in the morning edition of the bulletin (8:00 am). Similar to the winter of 2013/14, a delicate avalanche situation persisted for a long time this winter in the inner Alpine areas of Valais and Graubünden. Between 29.12.14 and 13.02.15, there was a considerable avalanche danger (level 3) throughout. The days with low avalanche danger (level 1) were concentrated at the beginning of December and the second half of March. At the turn of March/April, however, the avalanche situation was once again delicate.

Avalanche accidents and property damage

The number of all reported avalanche accidents up to April 15 was slightly higher than the average for recent years. However, two avalanche accidents with many fatalities (31.01.2015, Vilan, GR, 5 fatalities and 21.02.2015, Combe des Morts, VS, 4 fatalities) led to an above-average number of avalanche fatalities overall. The total number of fatalities for 15.04.2015 was 32, well above the long-term average. For the entire hydrological year, which lasts until September 30, 2015, the average value is 22 avalanche fatalities.

By April 15, 2015, 148 avalanches with 231 people recorded had been reported to the SLF for the winter of 2014/15. 31 people were injured in avalanches and 32 people lost their lives in 24 avalanche accidents. 11 people died at a predicted danger level 2 (moderate), 21 people at level 3 (significant). One person died in each of 21 accidents, 5 in one accident (Vilan, 31.01.2015), 4 in one accident (Combe des Morts, 21.02.2015) and 2 in one accident (Pointes de Tsevalire, 12.04.2015).

The avalanche victims were: Touring area: 22 people, Variant area: 10 people. 8 accidents with a total of 12 fatalities occurred in Valais, 8 accidents with a total of 12 fatalities in Graubünden, 3 accidents with a total of 3 fatalities in the canton of St. Gallen and also 3 accidents with a total of 3 fatalities in the canton of Bern. One accident with a fatality occurred in the canton of Nidwalden and in the canton of Uri. 27 avalanches resulted in material damage (to buildings, objects, forest) or search and evacuation operations were carried out (see Fig. 2).

This text originally appeared on the SLF homepage.

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