Purcells

Reports from Thursday include observations of explosives control in the central north of the region producing mainly storm slabs from size 1.5-2 on all aspects in the alpine. One remote triggered Size 1 persistent slab was also reported.

Wednedsday's reports included 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 showed a noticeable increase from previous days.

Some of the 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 is likely to increase toward the weekend with forecast warming.

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 old snow surface. Recent snowpack tests and avalanche activity show high 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. In the Purcells, both of these layers are of greatest concern in areas that received greater snowfall from recent storms.

Deeper in the snowpack, down about 90 to 150 cm, a rain crust from November is showing reduced reactivity in snowpack tests. This layer is considered dormant but it may be triggerable in thin spots around variable snowpack areas in the alpine.

Friday night: Scattered flurries bringing 2-5 cm of new snow. Light southwest winds.

Saturday: Mainly cloudy with continuing isolated flurries and a trace of new snow. Light west winds. Alpine high temperatures to -4, rising overnight.

Sunday: Mainly cloudy with thicker valley cloud due to a temperature inversion. Light variable winds. Freezing level to 2000 metres with alpine high temperatures to +1. Cooler at lower elevations.

Monday: A mix of sun and cloud with thicker valley cloud due to lingering temperature inversion. Light southeast winds. Freezing level to 2200 metres with alpine high temperatures to +3. Cooler at lower elevations.