Avalanche Forecast
Purcells
Neighbouring regions are experiencing large natural avalanche cycles and conditions are set for the Purcells to take their turn. Travel in avalanche terrain is not recommended.
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.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
20-30cm of recent snow is sitting on a range of variable surfaces 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.
Travel and Terrain Advice
- If triggered the storm slabs may step down to deeper layers resulting in large avalanches.
Avalanche Summary
Reports from Tuesday include several observations of Size 1 storm slab releases triggered by ski cutting and skier traffic near the centre of the region. Further to the north, explosives control yielded numerous Size 1-2 persistent slab results. Avalanche activity in neighbouring regions has been extensive and suggests a high point in a natural avalanche cycle on both the January 5 surface hoar layer as well as the December 15 surface hoar layer. Natural and remote (from a distance) triggers formed a large percentage of observations and sizes ranged from Size 1-3.5 (very large!). Activity was observed on all aspects and elevation ranges and the Lizard Range produced some of the more impressive observations.
Although avalanche activity has been less extensive in the Purcells, the region typically hosts fewer observers than in adjacent regions. The snowpack in the Purcells also shares the same basic structure as that of our neighbours to the east and west.
Looking forward, incremental loading from new snow on Thursday is likely to keep the region in an active pattern of avalanche activity that may intensify toward the weekend with forecast warming.
Snowpack Summary
Recent storms have brought 20-40 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 40-80 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. These weak layers are of greater 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, from sudden fracture characters to no result. This layer may be triggerable in thin spots around variable snowpack areas in the alpine.
Weather Forecast
Thursday: Cloudy with flurries bringing 2-6 cm of new snow. Light south winds. Alpine high temperatures to -9.
Friday: Mainly cloudy. Light southwest winds. Alpine high temperatures to -8.
Saturday: A mix of sun and cloud. Light west winds. Alpine high temperatures to -1
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40 to 80 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 potential exists in the Purcells.