Measurements
Measurements from around 90 stations of the Intercantonal Measurement and Information System and 80 other SwissMetNet stations operated by MeteoSwiss serve as sources of information.
Observer network
In addition, the SLF maintains an observer network consisting of around 200 observers trained by the SLF. These regularly transmit information - either stationary or from variable locations, e.g. from mountain guides - by conducting snow profiles and stability tests. The transmitted data includes parameters such as snow depth, amount of new snow, observed alarm signs and avalanches. Occasionally, an assessment of the avalanche situation is also provided. In addition, observations by local security services, the police, rescue organisations or winter sports enthusiasts serve as valuable sources of information.
Figure 1: Under Reply Public (https://pro.slf.ch/reply/public/#/), observations, images and comments can be reported directly to the SLF (source: Denis Pecaut 2024, Gepatschferner).
Weather
As the snowpack structure is significantly influenced by the weather, forecasts from weather models are used to assess the avalanche situation. Variables such as precipitation, wind, air temperature, radiation and humidity are required to assess the snowpack, its layering and (in)stability as well as changes to it. The ICON1 and ICON2 meteorological models from Meteo Switzerland are available for short-term developments. Models from the SLF's Operational Snow Hydrological Service (OSHD) are also used. The global meteorological model ECMWF, the European Centre for Global Medium-Range Weather Forecasts and general weather and precipitation forecasts from Meteo Switzerland also serve as a basis.
Synthesis and the finished product
The avalanche-forming factors - mainly weather, snow cover and terrain - are analysed by experts, the avalanche forecasters. In terms of terrain, altitude, exposure, slope inclination, terrain forms and ground cover play a decisive role. In addition to the data analysis, empirical values and specific combinations of these factors are also included in the assessment. The most reliable avalanche bulletin possible can only be created by combining and weighting the individual variables in a way that is appropriate to the situation.
The avalanche danger is determined from the stability of the snowpack, the distribution of danger spots in the terrain and the size, type and number of potential avalanches.
The finished product, the avalanche bulletin, can then be accessed via the internet or various apps such as White Risk or SnowSafe. It contains a detailed description of the danger levels and references to particularly dangerous terrain.
