This Tuesday morning, 3 departments of the Northern Alps are still placed by Météo-France on orange avalanche vigilanceat least until 10 a.m.: Savoie, Haute-Savoie and Isèrewhere almost a meter of snow has sometimes fallen since Sunday. This avalanche risk is assessed by the snow forecasters who work for Météo-France. These snow scientists are scientists who study snow and avalanches, analyzing what is called snow coverin other words the layer of snow.
To collect the data necessary for their calculations, snow experts use both automatic weather stationsbut also their own senses : they move around the ground, look at the snow, cut it up, touch it and listen to its sounds. Thanks to all these observations, they determine if in this snow cover, the snow is unstable and risks falling off. Everything obviously depends on the amount of snow fallenof humidityof the temperatureof vent a you mountain slope profile.
These clever calculations then make it possible to determine the risk of avalanches in the 37 mountainous areas of the country, for example Mont-Blanc, Vanoise or Maurienne. This risk is assessed on a scale of 1 to 51 being low risk. Level 4, high risk, results in orange vigilance, and level 5/5, very high risk, results in red avalanche vigilance. : this only happened twice, for example in Savoie in January 2018.
3 different types of avalanches
What complicates the forecast is thatthere are three different types of avalanches. First the powder avalanches : this is snow which has just fallen (and this is what we fear at the moment), which does not stick and which can break loose in the form of spontaneous avalanches, notably due to wind.
THE slab avalanches occur when the different layers of snow do not have the same consistency, for example dry snow covering wet snow or vice versa: a simple skier, even a light one, can then trigger the avalanche. Finally, the wet snow avalanches occur when the snow is saturated with water, when it melts, most often in spring or in the event of sudden mild spells and rain.
Furthermore, you may have already heard the term “snow flow” : this is a small avalanche. We use this expression in mid-mountains, in the Vosges, the Jura and the Massif Central, where avalanches are much rarer, unlike in the Alps and the Pyrenees. In all cases, great caution is required: no off-piste skiing or hiking without a guide!
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