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World of Science | Avalanche Bulletin

How is an avalanche bulletin created?

01/16/2025 by Lydia Knappe
An essential tool for off-piste skiing and ski touring is the avalanche report, also known as the avalanche bulletin. This has changed considerably over time. Not only does it appear more frequently - once or twice a day - but its spatial resolution has also become more detailed and precise. With the advance of artificial intelligence and the integration of model-based forecasts, new perspectives are opening up in avalanche warning.

In 1945, the Swiss Federal Institute for Snow and Avalanche Research (now the SLF) published its first avalanche report. As early as the late 1930s, the Swiss Ski Association published observations by the Commission for Snow and Avalanche Research on snow conditions in the Swiss Alps. During the Second World War and due to the military importance of the Alps, the topic of avalanches also became increasingly relevant at a political level. After the end of the war, the SLF took over the institutionalised avalanche warning, which is one of its most important additional products today.

Nowadays, the Swiss Avalanche Bulletin is published by the Avalanche Warning Service, which is based at the WSL Institute for Snow and Avalanche Research (SLF) . This allows the latest research results from the institute to be directly integrated and implemented. The bulletin covers the Swiss Alps, Liechtenstein and - if there is sufficient snow - the Jura. The bulletin has the character of a general warning.

Sources of information

Various sources of information are used to comprehensively address the heterogeneity of the snow cover and the dynamic behaviour of the snow and to enable predictions to be made. This data provides insights into previous developments, the current state and initial forecasts.

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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.

Procedure for creating an avalanche condition report

Three out of seven people at the SLF are responsible for preparing an avalanche condition report on a rotating basis. Data analysis of the information sources usually begins one day before the report is published with the help of geo-information-based programmes.

In the early afternoon, a briefing takes place in which the responsible avalanche warning officers present, compare and discuss their analyses. The bulletin text is reviewed during this meeting and adjusted if necessary. A hazard map is then drawn up showing the 120 Swiss warning regions, which are summarised into standardised hazard regions. The finalised report is then forwarded to a translation agency. The report is usually published at around 5.00 pm, while the translations into French, English and Italian are available online by 6.00 pm at the latest. The next morning at around 5.30 a.m., a new analysis of the night's developments, feedback from observers and changes in the weather forecast is carried out, after which the report is adjusted if necessary. The updated report is discussed again at a briefing at 7:00 a.m. and finally published at 8:00 a.m. in all four languages thanks to an automated translation catalogue.

Future prospects

In order to optimise the forecasting process and obtain a further independent opinion, model forecasts will be integrated into the preparation of the avalanche situation report from the 2024/2025 winter season. Snowpack simulations can be used to calculate stability and hazard probabilities as well as the probability of natural avalanches. Over the past two winter seasons, these modelled forecasts have been tested and compared with conventional human forecasts. The results so far show that the model predictions are very similar to human predictions and largely agree. The integration of artificial intelligence not only creates an additional objective perspective, but also the possibility of making the avalanche situation report more precise in spatial and temporal terms.

Figure 3: Overview of the decision tree for creating an avalanche situation report (source: SLF).

 

References:

Swiss Confederation: Blog Alert Knowledge. https://blog.alertswiss.ch/de/rubriken/gefahren/wie-entsteht-ein-lawinenbulletin/. [24.12.2024].

SLF: The avalanche bulletin. https://www.slf.ch/de/lawinenbulletin-und-schneesituation/wissen-zum-lawinenbulletin/wie-entsteht-das-lawinenbulletin/. [24 Dec. 2024].

SLF: History of the avalanche bulletin. https://www.slf.ch/de/ueber-das-slf/portrait/geschichte/die-anfaenge-des-lawinenbulletin/. [24 Dec. 2024].

Bilder: Denis Pecaut. denispecaut@hotmail.fr.

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