A large amount of new snow, strong winds, and a natural storm slab avalanche cycle on Tuesday indicate that the chance of human triggered avalanches is likely.
Natural avalanches have been reported with the new storm snow. Added flurries and wind will continue to develop slab properties and redistribute snow. The deepest and most reactive deposits will be in the alpine and around ridges and lee features at treeline.
Tuesday Night: Cloudy with scattered flurries, trace to 5 cm. Alpine temperature -5 C. Southwest wind 20-40 km/hr. Freezing level 500 m.
Wednesday: Flurries, 5-10 cm. Alpine temperature -3 C. South wind 25-45 km/hr. Freezing level 700 m.
Thursday: Snow, 10-25 cm. Alpine temperature -4 C. South wind 20 gusting to 50 km/hr. Freezing level 800 m.
Friday: More snow, heavy in areas, 10-30 cm. Alpine temperature -6 C. South wind 20 gusting to 60 km/hr. Freezing level 800 m.
A natural avalanche cycle to size 2.5 occurred sometime early 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.
Heavy snowfall blanketed 30-60 cm snow around the region. Flurries and snow through the week will continue to add to storm totals. South-southwest winds are redistributing fresh snow with deeper deposits around leeward terrain features.
The new snow likely covered a weak layer of surface hoar and/or a crust on south-southwest aspects, and is the failure plane for Tuesday's natural avalanche cycle. (Check out this MIN from Sunday before the snow started.)
Now down 40-90 cm, a second surface hoar layer is found under the recent storm snow and a 10-30 cm layer of older snow. Reports suggest this layer can be found on all aspects up to treeline elevations, particularly in areas sheltered from the wind. In the alpine, the recent snow covered hard wind slabs and/or sun crusts on south-facing terrain.
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.
