The snow cover in the Northern Alps improved considerably for Christmas with snowfall over the weekend above 1200 meters descending to low altitudes on Monday and Tuesday. This was followed by sunny weather which should continue until Saturday evening when further snow is expected. The snow certainly put a smile on the faces of many ski resorts which had reservations of only around 50% in the run-up to Christmas.
Snow blowing on ridgelines on Wednesday
On Tuesday afternoon snow was falling at a rate of around 5cm/hour in the Belledonne massif and was particuarly intense at mid-mountain altitudes (1000-1500 meters). The freezing weather brough traffic chaos to many areas with minor accidents as day trippers returning from the ski resorts found conditions considerably more difficult than when they set out.
The snow was heaviest in the pre-alps (west) with around half a meter of fresh snow over the week with about 30cm of snow towards the Italian border (Mont-Blanc, Haute Maurienne). It is possible to ski to 800-1200 meters depending on aspect and area. Fresh powder is to be found in forests and in sheltered bowls but the strong winds have reduced the snow cover on ridges and formed crusts and hard slabs elsewhere.
The clearing weather on Wednesday was accompanied by a fresh northerly wind which moved a lot of the fresh snow around at altitude. Slabs will have formed close to ridges and cols on southern slopes but backcountry travellers should also beware of soft slabs on northern aspects as the cold weather will mean that the snowpack will not yet have stabilized. The warm weather over the next two days will only slightly improve the stability of the snow pack.
There has been some natural avalanche activity on south facing slopes under the action of the sun and the warm weather (Isotherm to 3000 meters today and Saturday) this will continue. Some parts of the Isere will see a temperature inversion trapping colder air below 1500 meters, conditions that could lead to the formation of faceted crystals below this altitude and which may surprise skiers with snow sluffs as they climb into warmer snow.
A snowpit made late on Tuesday afternoon in the Belledonne at 2000 meters on a south-east facing slope showed 70cm total snow depth with about 30cm of fresh snow. This was sitting on a harder layer of about 8cm. Depth hoar was observed close to the ground. The snow cover is still quite thin and is not sufficient to bridge this weak layer. Meteo France reports that these conditions exist throughout the Northern Alps with a number of avalanches being triggered by the passage of skiers and snowboarders. Some of these are quite large – up to 80cm deep.
We have completed our office move but still do not have high speed Internet access so updates to PisteHors.com will be sporadic for the next couple of weeks.
References
Météo France issues daily avalanche bulletins for the French Alps, Corsica and Andorra. You should ideally consult at least the previous 5 days bulletins prior to your trip.
Henry’s Avalanche Talk publishes a daily translation of the Météo France bulletin for the Savoie area.