The “New snow” maps are published daily from 1 November to 30 June and updated several times per day. Three time periods are available: 24 hours, 48 hours, and 72 hours. The selected period can be adjusted continuously from the past into the future, ranging from 3 days in the past to 3 days in the future (this feature is currently only available in the WhiteRisk app). Periods longer than 24 hours are calculated as the sum of 24-hour new snow amounts.
The 24-hour retrospective for the current day is compared with measurement data for the first time at 8:30 a.m. and refined accordingly. Until that time, the new snow maps for the current day are based exclusively on model data. At 10:30 a.m., 4:30 p.m., and 10:30 p.m., the new snow analysis is updated again using the measurement data received in the meantime.
The new 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. In forecast mode, the new snow model uses data from the ICON forecast. In analysis mode, data from the ICON analysis are applied. Within the operational model system, the new snow model is updated whenever new ICON forecast or analysis data become available. Further details on the OSHD model system can be found in the information on the snow depth maps.
Differences between the amount and spatial distribution of modelled new snow and the ICON precipitation analysis and forecast arise in particular from the following aspects:
- ICON precipitation values represent the total observed or forecast precipitation in millimetres, whereas new snow heights represent the new snow in centimetres that is effectively present at the end of the 24-hour period, regardless of whether it fell on bare ground or on an existing snow cover.
- 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 at a spatially and altitudinally consistent assessment rather than a strict fit to individual local measurements. For very local information, it is therefore recommended 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 subsequently smoothed for cartographic representation. Time series for individual measurement stations can be viewed on the measured value map.