Wind slabs remain reactive to human triggering in exposed high elevation terrain. There is ongoing concern for the early-December deep persistent problem and we are now in a low probability, high consequence scenario with this layer.
Wind slabs remain reactive to human triggering in exposed terrain at higher elevations. Ongoing periods of strong wind continue add to these slabs. Expect them to be most reactive in steep, unsupported terrain features or places where the slab overlies a lingering weak layer.
The early December crust can be found down 100-150 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 cornice falls or smaller avalanches stepping down to this layer. Extra caution is recommended around thin snowpack areas and reloaded bed surfaces.
The ridge of high pressure is currently forecast to persist until Saturday with the next storm system arriving Saturday night.
Wednesday Night: Mainly clear with lingering valley cloud, light variable wind, treeline temperature around -8 °C.
Thursday: Mainly sunny with valley cloud, light SW wind, treeline high around -3 °C.
Friday: Mainly sunny with valley cloud, light SW wind, treeline high around -3 °C.
Saturday: Increasing cloud cover, light to moderate SW wind, treeline high around -3 °C.
On Tuesday, a variety of natural wind/storm slabs up to size 2 and cornices up to size 3 were reported but most of this natural activity had occurred on Monday or Sunday.
On Monday, wind slab avalanches on cross-loaded lee slopes produced natural avalanches up to size 2. A size 2.5 glide slab released near Revelstoke on south alpine slope due to strong solar input. Explosive control triggered a deep persistent size 3 avalanche in the Monsahees, with a fracture line of 120 cm deep.
Around Silverton area, a natural size 3 avalanche was reported Sunday on steep alpine feature. The failure was down to 100-150 cm the December facet/crust layer and ran full path. See the MIN report here.
Over the 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.
The snow surface is highly variable and consists of a crust at lower elevations and on solar slopes into the alpine, wind affected surfaces and wind slabs in exposed terrain, and settling powder in sheltered areas on polar aspects. Ongoing surface hoar growth up to 10 mm has also been reported in sheltered areas which is expected to be most prominent at elevations near the top of the valley fog layer.
The top 50-100 cm of the snowpack has a variety of persistent layers that may or may not remain a problem. The most recent snowfall covered a layer of surface hoar which is now down 20-30 cm. A layer of facets and surface hoar from early January is now down around 40-60 cm. The layer of facets from the end of December is now down close to 1 m.
The primary weak layer that remains a widespread concern across the Columbia Mountains is a deeply buried crust/facet layer that formed in early December. It is typically down 100-150 cm, but as deep as 200 cm in wind-loaded terrain. There has been regular avalanche activity on this layer at all elevations for over a month, but we are now seeing decreasing evidence since the recent warming event.
