The map shows only the wind data from IMIS stations of the SLF and from selected high-altitude (>1900 m) stations of MeteoSwiss. The high-altitude wind data recorded by these stations are representative of the prevailing wind conditions adjacent to ridgelines.
The wind can transport both fresh snow and loosely bonded old snow, and therefore exerts a major influence on avalanche danger.
The map shows the most recent available value for each station. If the most recent measurement was taken more than 210 minutes earlier, the station is greyed out and depicted without a value. Some of the depicted values originate from raw data that have not been checked or validated.
The following values are measured at the automated stations, mostly by propellers:
- Average wind speed: vectorial mean over 30 minutes
- Wind direction: direction of the vectorial mean
- Peak wind: maximum gust lasting 5 seconds recorded during the 30-minute measuring period. The recorded value is the wind speed. The direction is taken to be the vectorial mean over the entire 30-minute measuring period.
The automated stations of the SLF are solar powered, so that there is insufficient energy to heat the anemometers. In the presence of supercooled water droplets and wind, the sensors can become coated with hoarfrost. If the sensor data and meteorological parameters indicate that such conditions prevail, the data recorded by the wind sensors are ignored and no longer shown on the map. In some cases, the data captured by a sensor encrusted with hoarfrost can still be shown. In such instances, either the anemometer is not rotating and indicates a constant value for the duration of the hoarfrost, or it is rotating slower than the actual wind speed. The second of these two cases is very difficult to detect. This problem does not affect the heated SwissMetNet stations of MeteoSwiss (Le Moléson, Pilatus, Säntis, Les Diablerets, Jungfraujoch, Grimsel Hospiz, Titlis, Gütsch ob Andermatt, Les Attelas, Col du Grand St-Bernard, Eggishorn, Gornergrat, Monte Rosa-Plattje, Crap Masegn, Weissfluhjoch, Naluns Schlivera, Piz Martegnas, Buffalora, Piz Corvatsch, Passo del Bernina, Matro). They deliver reliable data even in conditions accompanied by severe hoarfrost.