Hazard will likely depend on the extent of cooling and new crust formation Thursday night. Storm slabs are expected to remain touchy up high where the snow remains dry, especially in wind loaded terrain. Use extra caution around steep south facing slopes if the sun is strong.
The early December crust can be found down 80 to 200 cm below the surface, with weak, sugary crystals (facets) on top of it. The likelihood of triggering an avalanche on this layer is decreasing but still remains a concern for avalanches stepping down. We are now in a low probability/high consequence scenario with this layer.
A reactive storm slab should be expected where the snow surface remains dry and crust-free at higher elevations. They will be most reactive in wind loaded terrain.
At lower elevations where the snow surface remains moist or wet, human triggered wet loose avalanches remain possible on steep slopes.
A ridge of high pressure brings dry and partly sunny conditions for Friday before a weak storm system arrives Friday night.
Thursday night: Partly cloudy, light variable wind, freezing levels dropping to around 500 m.
Friday: A mix of sun and cloud, light SW wind, freezing levels reaching as high as 1500 m.
Saturday: Snowfall up to 20 cm, moderate SW wind, freezing levels reaching around 1300 m.
Sunday: Periods of light snowfall, light to moderate SW wind, freezing level reaching around 800 m.
On Wednesday, natural storm slabs up to size 2.5 typically releasing down 20-40 cm, some of which were failing on a layer of surface hoar. Natural loose dry avalanches were being reported in extreme terrain at higher elevations and one loose wet avalanche was triggered at lower elevation. Humans and explosives were also triggering a variety of avalanches in the storm snow. On Tuesday, a variety of natural and human triggered avalanches up to size 2.5 were observed.
The persistent early December crust/facet layer has recently been active in this region. Concern for persistent slab activity like this is being sustained by new snow, wind, and warming. On Monday, a few very large simultaneous remote triggered persistent slab avalanches were reported in this Mountain Information Network (MIN) report south of Kaslo. It reported as a near miss, triggered from 150 m away on northeast through southeast features around treeline. The crown was one meter deep and propagated 500 m wide. On Friday, three naturally triggered size 2-3 avalanches on this layer were reported in mountain ranges just west of the Columbia river. They were reported at treeline and above on south and east aspects. Some were known to be wind slab avalanches that stepped down to this deeper, persistent layer in a thin, rocky area.
On Thursday, freezing levels climbed to at least treeline. With temperatures expected to drop on Thursday night, a widespread surface crust is expected to form. Below the new crust, 30-60 cm of recent storm snow is settling rapidly with the mild temperatures. This recent storm snow overlies the January 10 interface which may include weak facets and/or surface hoar. Another layer of facets from early January can be found down 60-90 cm.
We're still actively monitoring the early December crust. In some places, it's down 80 cm, while in wind-loaded terrain features it can be found as deep as 200 cm below the surface. It consists of faceted grains above a bulletproof crust formed by the Atmospheric Rivers of early December. There has been avalanche activity on this crust over the weekend. Larger avalanches in surface layers as well as natural cornice falls may still have potential to step down to this layer.
