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.
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
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.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.