Be careful around open slopes and convex rolls at treeline and alpine elevations. These slopes may have wind slabs and/or buried surface hoar layers.
Shifting wind over the past few days has likely blown snow into slabs in atypical terrain features. They could be especially reactive where they sit over a rain crust or large surface hoar crystals.
Reports suggest some slopes at treeline have a weak layer of surface hoar 30-50 cm below the surface. An avalanche cycle cleaned out this layer in many areas, but in places where avalanches have not yet run, it remains a concern. Use caution around convexities in open trees.
Two crusts with weak faceted grains overtop are buried deep within the snowpack. The upper layer is 80 to 130 cm deep and the lower is near the ground. A few large avalanches have run naturally on these layers recently. This problem is most prominent in thinner snowpack areas in the west of the region.
MONDAY NIGHT: Clear skies, light north wind, temperatures drop to -12 C.
TUESDAY: Sunny, light wind in the morning then moderate west ridgetop wind in the afternoon, treeline temperatures reach -5 C.
WEDNESDAY: Mix of sun and cloud, moderate northwest ridgetop wind, treeline temperatures around -5 C.
THURSDAY: Mostly cloudy, light wind, treeline temperatures around -8 C.
On Sunday skiers triggered a few small slab and loose avalanches (size 1).
Since last week's storm a few natural avalanches are suspected to have run on the surface hoar 20-40 cm down, including a size 2.5 storm slab out of a northwest facing gully feature around 2000 m near Nelson.
Last week, a widespread natural avalanche cycle up to size 2.5 was reported. A recent MIN report observed from Rossland shows a size 3 natural persistent slab avalanche that occurred during or post-storm.
10-15 cm of recent snow sits over a crust that extends to 2000 m, hard wind slabs at higher elevations, and large surface hoar crystals in wind sheltered areas around treeline. The upper snowpack is composed of some elevation-dependent permutation of crust sandwich formed by fluctuating freezing levels during the last storm.
A layer of surface hoar (and/or another crust) may be found 30-50 cm below the surface. Some recent avalanches are suspected to have run on this layer and where it has been found in snow profiles, it has been producing moderate to hard planar test results.
An older weak layer is buried 70 to 130 cm deep. It is composed of faceted grains over a crust. This MIN report observed from Rossland on Jan 13 shows a large natural slab avalanche failing on this layer during or post-storm. This suggests that it remains possible for riders to trigger this layer. Another layer of faceted grains above a melt-freeze crust that formed in early November is upwards of 200 cm below the surface. This has been the suspected failure layer of a few very large avalanches that released last week in the Rossland range.
