The "Snow depth" map is published from 1 November to 30 June at around 7 am.
The snow maps are based on the snow modelling of the SLF's Operational Snow Hydrological Service (OSHD). The OSHD model system uses high-resolution meteorological input data from weather forecast models and various reanalysis products from MeteoSwiss. As part of the operational modelling system, the snow model is updated every time new forecast and analysis data from COSMO becomes available.
The model chain essentially comprises the following model steps:
- Downscaling of the meteorological input data from COSMO from 1 km to 250 m resolution. Radiation information is dynamically adjusted using a 25 m resolution terrain model to take into account topographical influences such as shading and slope inclination. For wind, the influence of the local terrain on the wind is taken into account.
- Division of total precipitation from COSMO into solid and liquid form using air temperature data.
- Altitude-dependent calculation of fresh snow density taking into account air temperature and wind speed. This function was optimised by calibration based on measurements of the density of freshly fallen snow that has settled over 24 hours.
- Assimilation of snow measurement data from around 440 automatic weather stations and observers.
- Physical modelling of various snow processes, such as a) Settlement of fresh snow and snow cover due to its own weight, b) Melting of fresh snow when it falls on apery and still warm ground, c) Melting of snow in the event of significant warming or rain, d) Snow processes in the forest.
The data is modelled for the whole of Switzerland with a resolution of approx. 250x250 m and smoothed for display.
A time chart of the data from individual measuring stations can be viewed on the measured value map.