Over 1m new snow this week. How stable is the base layer in the snowpack?

Today it started snowing again. This is also accompanied by significant amounts of wind blowing in from the west. We are expecting 20 to 50cm of snow in the next 12 hours (depending on which part of the N French Alps you are in. Less snow in the east and more in the west). Then we expect another 10-20 cm on Wednesday night and then up to 1m of snow on Friday and Saturday

This snow is falling on a base layer of old snow. So it is helpful to understand what the characteristics of that layer are. Will the new snow bond to the base layer? Is this base layer going to become a persistent weak layer under the new snow that is falling this week.

In this video filmed yesterday, we examined the snowpack at 2400m on a North Facing slope above Tignes 1800m.

The snow felt like it was a mixture of rounds that would hold together with some angular grains weakening it. But on the whole it felt like it was not surface hoar, it might well form a stable base under the new snow.

Meteo France confirmed this and reported that the snowpack is a mixture of well-bonded snow and some angular grains or facets that could become a weak layer. They seemed to be unsure of how this will evolve.

In a conversation with one of the Val piste patrol, they are equally unsure. We have not had a lot of cold weather, it is likely that the temperature gradient in the snowpack was quite low, so the snow could be holding up well. What he was more worried about is the volume of snow (1m+) this week, coupled with significant wind transport, so leeward slopes with wind loading will be unstable. He commented that wind transported snow is less bonded and more unstable.

It is also likely that the high north -ish facing slopes (>2400m) on the French Italian border and below ridges will have experienced colder weather and have suffered from a steeper temperature gradient. So there may be more angular grains and faceted snow causing a weakness on these slopes.

Weather outlook

Tuesday morning will be a sunny day with a lot of fresh powder. However much of it is likely to have been affected by the west wind. Be cautious on wind loaded slopes.

Wednesday will still be clear weather before more snow Wednesday night. The big snowfall is expected Friday and Saturday.

Read the avalanche bulletins for up to date information

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