Purcells

Moderate to heavy snowfall on Friday is expected to continue overnight into Saturday morning. Expect 10-15 cm in the North of the region and closer to 20 cm in the South by Saturday noon. The freezing level should remain at about 800 metres during the storm and then drop down to valley bottoms by Saturday evening. Winds are forecast to be moderate to strong from the South until about midnight and then ease a bit and clock to the west for the morning hours of Saturday. Expect to see some convective flurries on Sunday as a ridge of high pressure slides in behind the storm bringing light northerly winds by late in the day. There may be some sunny breaks on Sunday, and mostly clear skies and cooler temperatures for Monday.

The recent natural cycle is reported to have ended, but human triggering continues to be likely from light additional loads. Avalanches continue to be triggered remotely by large loads like helicopters landing on ridges adjacent to avalanche terrain. The wind and new snow combined to overload the buried persistent weak layer (PWL) on Wednesday. Widespread avalanches were reported from many operators in the region. Some large avalanches up to size 3.5 were reported from the Bugaboo Range. Some avalanches released in very low angle terrain in cut blocks below treeline. A couple of slides released down to the basal facet layer near the ground. Please look at the Special Avalanche Warning that was issued today.

Light new snow and southeast winds during the day on Friday are forecast to become moderate southwest wind and moderate snowfall overnight resulting in about 15 cm. Recent strong gusty winds have developed stiff windslabs at all elevations. The upper snowpack structure is very complex. There are buried layers of surface hoar, buried melt-freeze crusts, and some buried crusts with facets. These weak sliding layers are buried anywhere from 30 - 70 cm by several different storm layers. There are some shears in the storm layers on decomposed and fragmented snow crystals. As the snow above the surface hoar layers settles into a cohesive slab, we are seeing easier and more sudden shears that are a bit deeper. The surface hoar is more likely to produce wider propagations, and lower angle fractures in areas where it is associated with a crust. The crust has been reported to be 2-3 cm thick in some areas. The mid-pack is generally well settled. Basal facets have not been reactive, but operators continue to monitor this layer in tests. Triggering this deep persistent weak layer is unlikely, but shallow snowpack areas or shallow weak areas adjacent to deeper wind loaded slopes are the most suspect locations.