Avalanche Forecast
Purcells
Very dangerous avalanche conditions have developed in the Purcells. The danger is greatest in areas that received more snow from recent storms.
A Special Public Avalanche Warning is in effect in this region.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.
- Numerous large avalanches have run on this layer in well supported, treed terrain.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
20-60 cm of recent snow is sitting on a weak layer and it will need more time to form a solid bond to them. The new snow is especially reactive where it has been affected by the wind. The danger is greatest in areas that received the most new snow.
Travel and Terrain Advice
- If triggered the storm slabs may step down to deeper layers resulting in large avalanches.
- The new snow overlies a persistent weak layer and will take longer than usual to stabilize.
Avalanche Summary
Reports from Wednesday include observations of several persistent slab releases from Size 1-2.5 that were primarily triggered remotely (from a distance) and failed at the December 15 interface. Several other storm slabs and wind slabs were triggered, naturally, remotely and by skier traffic. Reports have been focused in areas that received more snow from recent storms and show a noticeable increase from recent days.
Some of the notable themes that are emerging from recent activity both in the Purcells as well as in neighbouring regions include accidental and remote triggering, 'step down' release types, releases on surprisingly low angle, supported terrain, as well as wide fracture propagations.
Looking forward, expect a continuation of heightened human triggering potential that may increase toward the weekend with forecast warming.
Snowpack Summary
Recent storms brought a variable 10-60 cm of new snow to the region. The new snow sits on surface hoar on sheltered slopes as well as sun crust on steep solar aspects. Moderate to strong southwest winds accompanied the snowfall at higher elevations, creating wind slabs in lee features.
As the new snow continues to consolidate, it is forming a dangerous slab above several persistent weak layers that exist in the snowpack. The first of these is the surface hoar found at the new snow interface. Recent snowpack tests and avalanche activity show a high degree of reactivity at this layer. Below it, the December 15 surface hoar is now buried a widely variable 40-100 cm deep. This layer has been the failure plane in many recent destructive slab avalanches in neighbouring regions and its reactivity has been most apparent at treeline and below treeline. In the Purcells, both of these weak layers are of greatest concern in areas that received greater snowfall from recent storms.
Deeper in the snowpack at depths of about 90 to 150 cm, a rain crust from November is producing variable snowpack test results. This layer may be triggerable in thin spots around variable snowpack areas in the alpine.
Weather Forecast
Friday: Mainly cloudy with isolated flurries and a trace of new snow, continuing overnight. Light southwest winds. Alpine high temperatures to -6.
Saturday: A mix of sun and cloud. Light to moderate west winds. Freezing level rising to 1600 metres with alpine high temperatures to -2. Mild temperature inversion.
Sunday: Mainly sunny with valley cloud due to a temperature inversion. Light southwest winds. Freezing level to 1800 metres with alpine temperatures to +2. Cooler at lower elevations.
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40 to 90 cm of snow now sits above a touchy weak layer. Remote and natural triggering has become a regular occurrence. Widespread avalanche activity has occurred on this layer in nearby regions and similar activity is now being reported from Purcells