Resources used to produce Avalanche Bulletins|
The SLF Avalanche Warning Service uses a variety of resources to compose the Avalanche Bulletins:
* About 180 observers with an array of measurement programmes (measuring, observing, evaluating) who report between 6.00 and 8.00 am each morning, sometimes also at midday
* About 100 automated measurement stations (intercantonal measurement and information system (IMIS), supplementary measurement network (ENET)) and data collected by about 70 additional ANETZ (automated network) stations operated by the Swiss meteorological office, MeteoSwiss
* Every two weeks, about 50 flat-field and 50 slope profiles with stability tests
* Forecasts of various weather services
* Questionnaires for reporting avalanches and evaluating avalanche danger
Three typical observer groups are the "Observer station Observers," the "Regional Observers" and the "Measurement Station Observers." At the Observer stations, observers report the key weather conditions (including precipitation and clouds) and snow characteristics (new snow, overall snow depth, sink-in depth, new snow density, snow temperature, snowpack, structure of snow surface) on a specific sampling area, while Regional Observers assess similar variables within their area without specific sampling areas. In addition, members of both groups report their observations, e.g. released avalanches, alarm signals, as well as their assessment of the avalanche danger. At the Measurement Stations, only new snow and the snow depth are measured. These measurements serve climatological purposes, by and large. Observers are located throughout the entire Swiss Alps; their measurement and observation posts are located at altitudes of 1000 - 2700 metres above sea level, as well as lower-lying measurement stations.
The hourly and half-hourly measurements of the automated ANETZ and ENET stations of MeteoSwiss and the various IMIS "automated snow measurement stations" operated in collaboration with the responsible agencies of the mountain cantons have also proven highly useful in the analysis of avalanche danger.
Another major technical resource is the approximately 50 slope and 50 flat-field profiles that are taken every 14 days. Their locations are distributed throughout the entire Swiss Alps. These profiles are produced by observers in the experimental flat fields and on representative test slopes in conjunction with rutschblock tests.
A variety of "forecast aids" produced by MeteoSwiss and Germany's National Meteorological Service (DWD), as well as other providers' aids as necessary, are used to evaluate the short-term weather prospects.
To analyse the avalanche danger, a knowledge of both the basic relationships between weather and the snowpack and the relationships between snow layering and avalanche activity are essential. The avalanche expert makes decisions primarily on the basis of assessing the anticipated snowpack stability. The interaction between stress and strength in the ever-changing snow is highly complex. Especially critical attention is devoted to the influences of precipitation, wind, temperature and snow layering, to name but the most significant elements. The practical implications for the terrain (altitude zone, aspect, type of terrain) arising from these deliberations are then assessed.
The Warning Service uses visualisation software to manage the large volumes of data and information that arise. This software also supports the production of additional supporting products, such as New Snow and Snow Depth Maps.
Finally, some pragmatic decisions need to be taken when the Bulletins are being produced. Despite the ever-increasing support provided by electronic aids, the long-standing personal experience of the Avalanche Warning Service's employees remains indispensable.
Avalanche Bulletins are addressed to all those who are exposed to possible avalanche danger in the mountains in winter, whether engaging in professional or recreational activity. This includes members of the following groups:
* Avalanche warning services and avalanche committees of district authorities, civil engineering offices and mountain railway and cableway operators
* Police and rescue services
* Residents of mountain villages
* Skiers and snowboarders
* Backcountry skiers, snowshoe hikers
* Mountain guides and snow sport instructors
* Mountain and ice climbers
* Armed forces
Fatalities due to avalanche burial in Switzerland average 25 persons annually over the long term. Accident analyses demonstrate that most avalanche victims come to grief in "open terrain"; that is to say, while practising leisure activities on skis, snowboarding or mountain climbing. Their share of fatalities in the last 10 years amounted to more than 90%. Of these victims, about 90% triggered the avalanche themselves or it was released by another member of the same group.
The Avalanche Bulletin is intended as a preventive warning; it provides assessments for a wide public (see above). Despite its limited scope, the Avalanche Bulletin must address a variety of user groups, depending on the specific situation. This can result in a Bulletin in which, for example, in relatively stable snow and weather conditions, the warnings for backcountry skiers are more elaborate than those for the local avalanche safety services. In times of "high" and "very high avalanche danger", when it can be assumed that backcountry touring is ruled out or extremely restricted, the recommendations for the avalanche safety services are more extensive.