The avalanche bulletin ¶

The WSL Institute for Snow and Avalanche Research SLF uses the avalanche bulletin and various supporting products to inform the public about the current snow and avalanche situation in the Swiss Alps and in the Jura. The content of the avalanche bulletin is designed as an informed warning. It is published one to two times a day in winter and primarily contains a forecast of the avalanche danger in the Swiss Alps, Liechtenstein and, when there is sufficient snow cover, the Jura as well.

Additional information about the weather's effects in terms of avalanches and the condition of the snowpack gives users a clearer picture of the current situation and provides a basis for making their own assessment, as the information provided the avalanche bulletin cannot take the place of their own local on-site assessment. The information contained in the bulletin is too general for this because of the limited data it is based on.

Target audience

The avalanche bulletin is aimed at all those who are exposed to potential avalanche danger in the mountains in winter, whether in a professional or recreational capacity, and those who are responsible for the safety of others. This includes members of the following groups:

• Avalanche services and committees of the communal authorities and civil engineering offices, as well as the safety services of the mountain railway/cableway operators
• The police and rescue services and the armed forces
• Mountain guides, snow sports instructors and backcountry tour guides
• Residents of mountain villages
• Winter sports enthusiasts away from secured ski runs, such as freeriders, backcountry skiers, snowshoe hikers, mountaineers and ice climbers
   

When the snow and avalanche situation is relatively favourable, the avalanche bulletin will mainly contain information for winter sports enthusiasts. From danger level 3 (considerable) upwards, information for the avalanche warning services is issued more frequently. At the very high avalanche danger level (level 5), when snow sports are hardly possible anyway, the avalanche bulletin will mainly contain information for the avalanche warning services.

Structure of the avalanche bulletin

In high season the structure of the avalanche bulletin is based on the 'information pyramid', i.e. the most important comes first (danger level), followed by details of the locations where the danger level applies and then the avalanche problem, the danger description and information about the snowpack and the weather. Finally, measured data can also be displayed. The use of standardized terminology aids both understanding and implementation.

Individual parts of the avalanche bulletin

The avalanche bulletin consists of a zoomable hazard map, including a hazard description and a section headed "Snowpack and weather". A description of this content is given below. In the off-peak periods and during large snowfalls in summer, the avalanche warning service usually has less information available than in winter. Then the avalanche bulletin is less detailed, and areas with danger level 1 (low) are usually not described.

Avalanche danger

The avalanche bulletin's most important component is its avalanche danger forecast. This comprises the following aspects:

Danger level and avalanche prone locations

The danger of dry and wet avalanches is assessed separately. The danger level indicated is based on the five-point European avalanche danger scale. When there is a moderate or higher danger of dry avalanches (starting at level 2), the points on the scale are also subdivided (-, =, +). In most cases, the endangered aspects and altitude zones are pinpointed as well. If such information is not given, the indicated danger level applies to all aspects and altitude zones. Warning regions are grouped together whenever an identical danger level (in identical aspects and altitude zones) applies, provided that the avalanche problems are also the same and the dangers can be described appropriately for all the affected regions. The danger description may contain additional information concerning terrain types that are particularly affected.

On the danger map, the maximum expected danger level is shown for each warning region (maximum of dry and wet danger). If the danger level is likely to change during the day, the danger level is normally based on the situation in the morning. In typical springtime conditions, two maps show both the more favourable morning situation and the more unfavourable situation in the afternoon (double map).

Avalanche problems

Often the avalanche danger is classified as falling under one or more of the five 'typical avalanche problems'. Normally the avalanche bulletin assigns the situation to one or more of these categories. The following problems are distinguished:

Dry-snow avalanches

• New snow (considerable snowfall in recent days)
• Wind slabs (snow transported by the wind)
• Old snow (weak layer(s) prone to triggering within the old snowpack)

Wet-snow avalanches

• Wet snow
• Gliding avalanches

If there is no conspicuous avalanche problem (often when a low avalanche danger (level 1) applies), the situation is described with the text "no distinct avalanche problem".

Danger description

There is a specific danger description for each danger region marked on the map, with the danger of dry and wet avalanches being described separately. The danger description reflects the conditions in the altitude zones and aspects where the danger level applies. Outside these altitude zones and in other aspects it can be assumed that a fundamentally similar, but more favourable, avalanche situation exists. In other words, the avalanche prone locations are likely to be found less frequently in these places. Among other factors, the danger description can contain information concerning the likelihood of release and the size of the anticipated avalanches or relating to the snowpack structure. If necessary, remarks or recommendations for individual groups of users are also provided.