The “Snow depth” map is published from 1 November to 30 June at around 7:00 a.m.
The snow maps are based on snow modelling by the SLF’s operational snow-hydrological service (OSHD). The OSHD model system uses high-resolution meteorological input data from numerical weather prediction models as well as various reanalysis products provided by MeteoSwiss. Within the operational model system, the snow model is updated whenever new ICON forecast or analysis data become available.
The modelling chain essentially consists of the following steps:
- Downscaling of ICON meteorological input data from a 1 km to a 250 m spatial resolution. Radiation information is dynamically adjusted using a digital terrain model with a resolution of 25 m to account for topographic effects such as shading and slope inclination. For wind, the influence of local terrain on the wind field is taken into account.
- Local calculation of new snow density considering air temperature and wind speed. This function has been optimised through calibration using measurements of the density of freshly fallen snow that has settled over a 24-hour period.
- Physical modelling of various snow processes, including a) settlement of new snow and the snowpack under their own weight, b) melting of new snow when it falls on bare and still warm ground, c) snowmelt during warming or rainfall, d) snow processes in forested areas.
- Assimilation of snow measurement data from around 440 automatic weather stations and observers. The model does not necessarily reproduce local measurements exactly at the measurement sites, as data assimilation aims to provide a spatially and altitudinally consistent assessment rather than a strict fit to individual local measurements. For very local information, it is therefore advisable to consult the measurement data directly.
The data are modelled for the whole of Switzerland at a spatial resolution of approximately 250 × 250 m and are subsequently smoothed for cartographic representation.
The map provides information on snow depth and the degree of snow cover. Areas that are only partially covered with snow (less than 60% of the area covered with snow) are shown dotted.
Time series of data from individual measurement stations can be viewed on the measured value map.