Three departments in the Southern French Alps, the Alpes Maritimes, Alpes de Haute-Provence and the Hautes-Alpes are on avalanche alert for Wednesday 28th January. Up to 70cm of fresh snow accompanied by strong winds is expected in the Hautes-Alpes and the avalanche risk is High (4/5) across the region. The avalanche risk is also 4/5 in the Oisans.
Meteo France see the principle risks as fresh snow falling on a persistent weak layer (PWL). We've been warning about this PWL in the region since early November. Local ski tourers have been surprised over recent days by the extent and nature of avalanche activity, including in woods.
The forecasters are particularly worried natural avalanches during the night from Tuesday to Wednesday and on Wednesday morning, as heavy snowfall is accompanied by strong winds. Medium to large avalanches will become widespread in the middle of the night as snow accumulation became significant. A very large avalanche cannot be ruled out at the highest altitudes of the massif, in an area of heavy accumulation due to southerly winds. This natural activity will subside by midday on Wednesday.
For back-country enthusiasts they warn that the snow-pack is very unstable. Numerous slabs will form due to heavy snowfall overnight from Tuesday to Wednesday and on Wednesday morning combined with heavy snow transport by the wind. These will be very easy to trigger with thick with large breaks likely on all orientations above 1600 to 1800 meters. Powdery in appearance and therefore difficult to spot. They can cause medium to large avalanches (size 2 to 3). A very large avalanche (size 4) cannot be ruled out at high altitude and/or in the event that a deeper persistent weak layer buried is triggered, particularly on shaded slopes (west, north, east).