Incoming weather is not conducive to natural avalanche activity, but human-triggered avalanches are possible. Uncertainty remains about this difficult-to-forecast deep persistent slab problem.
Expect to find lingering wind slabs on wind-affected slopes at higher elevations, and anywhere a slab forms over a crust or surface hoar layers. Wind slabs are more prone to be triggered on steep, convex and unsupported slopes, especially on lee features.
The early December crust can be found down 100-200 cm below the surface, with weak sugary crystals (facets) on top of it. Large avalanches have been observed at all elevations including some unusual areas such as the middle of slide paths, open trees, and burns. Although the likelihood of triggering an avalanche is decreasing, there is an ongoing concern for smaller avalanches stepping down to this layer.
An upper ridge over the province is giving dry conditions for the next couple of days, although some low clouds will persist in interior valleys. It will gradually start shifting east by Friday morning, opening the door for a change in the weather pattern for the weekend.
TUESDAY NIGHT: Cloudy with clear periods / Light west wind gusting 40 km/h / Low temperature -6 C / Freezing level at valley bottom.
WEDNESDAY: Cloudy with sunny periods / Moderate northwest wind / High temperature -8 C / Freezing level at valley bottom.
THURSDAY: Mix of sun and clouds / Light west wind / High temperature -4C / Freezing level at valley bottom.
FRIDAY: Mix of sun and clouds / Moderate southwest wind / High temperature -2C / Possible temperature inversion / Freezing level at 1000 m.
On Monday, wind/storm slabs avalanches (up to size 1.5) were reported throughout the region; both intentionally and accidentally triggered by riders on convex features or steep slopes. Wind, warm temperatures and solar radiation have created a recent avalanche cycle (up to size 2) within the upper snowpack layers. Cornice falls were also suspected to have pulled out slabs. In the Selkirks, two very large deep persistent (size 2.5- 3) slab avalanches were also reported from various alpine aspects, which have released naturally on the December facet/crust layer.
This past week, numerous very large (size 2.5-4.5) deep persistent slab avalanches occurred in both the Selkirks and Monashees. These avalanches failed on the early December facet/crust layer, typically 100-150 cm deep. This layer is likely to plague our snowpack for the remainder of the season and will be a low probability but extremely high consequence result if triggered.
A variety of snow surfaces can be found: crusts at lower elevations and on solar slopes into the alpine, wind press and wind slabs in open and exposed terrain, and settling powder in sheltered areas. Surface hoar growth has also been reported at the surface and within the upper snowpack in sheltered areas
The most recent snowfall covered a layer of surface hoar now down 20-30 cm, likely responsible for the most recent natural storm slab avalanches reported Jan 20-21. The upper snowpack (top 30-100 cm) include a layer of surface hoar and crusts as well as facets formed at the start of January.
The primary weak layer that remains a widespread concern across the Columbia Mountains is a 100-200 cm deep crust/facet layer that formed in early December. There has been regular avalanche activity on this layer at all elevations for over a month.
