40-70 cm snowfall this week has buried a weak layer of surface hoar. With additional loading from new snow and wind, there is a high likelihood of human triggered avalanches.
40-70 cm new snowfall this week has covered a weak layer of surface hoar. Ongoing snow and flurries will continue loading the snowpack as wind redistributes loose snow and develops slab properties. This has developed a potentially reactive and widespread avalanche problem that is likely to be triggered by skier traffic.
Thursday Night: Flurries, 5-15 cm. Alpine temperature -4 C. South wind 20-30 km/hr. Freezing level 500 m.
Friday: Snow, 10-15 cm. Alpine temperature -2 C. South-southwest wind 25-45 km/hr. Freezing level 800 m.
Saturday: Snow and flurries, 5-15 cm. Alpine temperature -3 C. Southwest wind 25-45 km/hr. Freezing level 700 m.
Sunday: Flurries, up to 10 cm, Alpine temperature -5 C. Southwest wind 10-30 km/hr.
A natural avalanche cycle to size 2.5 occurred Tuesday, in steep and leeward terrain at treeline and above. In many cases avalanches failed with input from strong to extreme south and westerly winds gusting upwards of 70 km/hr.
Natural storm slab avalanches to size 1.5 were observed around treeline on Wednesday and loose, dry snow was running from steep alpine features. Avalanche control work Wednesday and Thursday triggered numerous large (size 2) avalanches with explosives, crown depths ranged from 30-80 cm.
As the loose snow gains cohesion and more flurries increase the load on a touchy surface hoar layer, the new snow may be quite reactive to skier triggers.
Heavy snowfall blanketed 40-70 cm snowfall throughout the region this week. The new snow covered a weak layer of surface hoar, old faceted surfaces, and a crust on south/southwest aspects in the alpine. The natural avalanche cycle on Tuesday reported slabs failing at this interface. South-southwesterly winds have developed wind slabs, especially around ridge features and into the alpine.
Reports from the Shames area suggest the surface hoar layer is prevalent on all aspects at treeline elevations down to 800 m, and more likely on leeward and sheltered alpine areas. Ongoing snow and flurries are adding more load and stress to this layer. Check out this MIN report from sheltered terrain near Shames.
The lower snowpack is generally considered strong, as there has been very little to report in terms of recent avalanche activity or snowpack test results on deeper layers. Snowpack depths at treeline range from 100-200 cm and taper quickly at lower elevations.
