Conditions may have improved, but be mindful that deep instabilities are still present. Avoid shallow or variable depth snowpacks and unsupported terrain features.
Recent wind slabs have been reactive where it overlies surface hoar. Along with suspect layers in the upper snowpack, expect to find lingering wind slabs on wind-affected slopes at higher elevations, and anywhere a slab forms over crust or surface hoar layers.
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 ongoing concern for smaller avalanches stepping down to this layer.
MONDAY NIGHT: Partly cloudy / Decreasing northwest wind / Low temperature -10 C / Freezing level at valley bottom.
TUESDAY: Increasing cloud / Light flurries / Light west wind gusting moderate / High temperature -6 C / Freezing level around 700 m.
WEDNESDAY: Cloudy with sunny periods / Light west wind gusting moderate / High temperature -8 C / Freezing level around 700 m.
THURSDAY: Mix of sun and clouds / Light northwest wind / High temperature -5 C / Possible temperature inversion / Freezing level around 500 m.
On Sunday, warm temperature and strong solar radiation naturally triggered a large (size 2.5) deep persistent avalanche from steep rocky alpine features in the Selkirks. In the Monashees, a cornice fall was large enough to trigger an avalanche at the top of the track zone, which has propagated full path. It has likely involved the Dec 1 deep persistent layer.
Wind slabs have shown signs of surprising reactivity throughout the region, with a remote human trigger avalanche over a large convex rollover 100 m away, probably failing on a surface hoar layer. Numerous small accidentally triggered wind slabs were also reported on the same layer down 30-45 cm.
On Saturday, explosives near the Trans Canada triggered very large avalanches (size 2.5-3.5) failing on the early December facet/crust layer. This included a historical size 4.5 avalanche which started at ridgeline, created new trim lines, and destroyed mature timber.
This past week numerous very large (size 2.5-3.5) 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. One notable pattern is that many of these avalanches released at relatively low elevations (1700 to 2000 m) in open clearings, burns, and slide paths. In many cases, they were triggered by smaller avalanches starting at higher elevations. 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.
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) has a variety of layers that may or may not be a problem. These layers include surface hoar and crusts buried during January snowfalls and facets buried at the start of January. While none of these upper layers are necessarily going to remain a long-lasting concern, there is uncertainty about their spatial distribution and their remaining reactivity after the warm event.
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.
