Posted on: 2014-04-30 12:52:06 by davidof

Review of the Swiss 2013/2014 snow and avalanche conditions

The Swiss Snow and Avalanche Research Institute has published its review of the 2013/14 snow and avalanche situation. Mild weather, strong winds and a localized critical avalanche situation characterized the season.

The Swiss 2013/2014 winter was one of contrasts: an extraordinary amount of snow on the southern side of the Alps but with a mostly stable snowpack. Very few days of snow on the Central Plateau. The Valais and Grisons saw an exceptionally long a critical avalanche situation.

“Winter, What winter?” In the Swiss central plateau and in a broad arc from Zurich to Geneva the overall impression was that winter was over before it even started. Contrast that with the Southern Alps which groaned under heavy snow from Christmas and which saw twice the long term average precipitation. Many areas in Ticino, the Upper Engadine, the Southern valleys of the Grisons saw fresh snow records during January and February. However viewed over the whole winter nowhere saw absolute records for snow depths.
Central Lowlands - worst winter since 1989/90.

The winter period (from November 2013 to March 2014) was 1 - 1.5° C warmer than the long term average. This meant that some places in the Central Lowlands saw no snow days at all, that is a day where more than 5cm of new snow is recorded. Only the winter of 1989/90 was worse. Although only a few snow days were recorded at low altitudes in the Southern Alps they were still much better than elsewhere. Locarno (on the mild Swiss/Italian lakes) saw 7 snow days, more than twice the number in Zurich. One reason for the mild conditions were frequent strong South to South-West winds. This caused foehn conditions in the north with a lot of snow transport onto north facing slopes, increasing the risk of slabs there.

Most areas only had thin snow cover through to Christmas. This had transformed into a weak layer of large, loose crystals during the month. When this layer was covered by subsequent snowfall it was like a a house of cards at the base of the snowpack. Between Christmas and the New Year it was a major cause of avalanches triggered by backcountry enthusiasts. The Southern Valais and North Grisons saw an exceptionally long, up to two months, period of considerable avalanche danger (⅗). In the Southern Alps the depth of snow isolated the weak layer. Avalanches mainly occured in the upper layers of the snowpack which were weakened during the repeated, often heavy, rainfall.

Compared to the long-term average the winter of 2013/14 saw slightly less avalanche danger overall. Principally risk level 2 (Moderate) followed by risk level 1 (Weak). Level 1 days were predicted twice as often compared to the average, level 2 days slightly less than average. The delicate period with the hazard levels 3 and 4 was focused primarily from late December to late February. To mid April 2014 the SLF had reports of 104 avalanche incidents with 152 victims completely buried. Of these 17 were injured and there were 17 fatalities. The death toll is slightly below the long term average.