Numerous natural wind slabs and the occasional deep slab avalanche have been the pattern over the last couple of days and the next few days to come. Use good judgment and resist being lured into or near steep terrain.
Moderate to strong W-N winds have formed wind slabs in lees areas of the alpine and treeline. In the past couple days these wind slabs have been reactive to skier traffic, and have failed naturally with ongoing wind loading.
The lower snowpack is comprised of weak facets and depth hoar with the upper snowpack forming a 40 to 90 cm thick slab above the weakness. In the alpine and treeline, recent strong winds have created a stiff slab over the weaker facets below. Human triggering remains a concern anywhere this weak layer is present.
Over the past few days, there have been reports of numerous windslab avalanches to size 2, cornices failures triggering avalanches, and deep persistent avalanches to size 3. On Tuesday, Sunshine patrol triggered a size 2.5 avalanche with explosives released on the ground in the deep persistent layer. In the past few days, in Yoho, a deep persistent slab avalanche was observed on Mt. Carnarvon (size 3) and on Mt. Field (size 2.5). The Mt. Field avalanche ran to within 200m of the Kicking Horse River. The Mount Lefroy avalanche also scrubbed to ice in some locations.
Moderate to strong W-N winds have formed wind slabs at treeline and in the alpine. Below this, the upper snowpack contains weak layers 20-40 cm deep (Jan. 4th) and 30-60 cm deep (Dec. 17th) that are generally unreactive. The Nov 16 deep persistent layer is down 40-90 cm and continues to produce variable sudden test results. In areas west of the divide, the snowpack is more supportive than in eastern areas.
Expect strong Westerly winds for the next few days. Some light flurries start Wednesday morning with up to 5-10 cm expected along the Continental Divide and west. Alpine temperatures will be in the -10 to -15C range for Wednesday and -5 to -10 C range for Thursday and Friday.
More details can be found in the Mountain Weather Forecast
