Regions
Kootenay Boundary.
Lingering wind slabs are expected to remain reactive to human-triggering on Tuesday at higher elevations. A weak surface hoar layer down 40-70 cm may still be reactive and should still be treated with respect.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Mostly cloudy conditions are expected for Tuesday with sunny breaks and light isolated flurries both possible. Afternoon freezing levels are expected to be around 1300m and alpine winds are forecast to be light from the southwest. A mix of sun and cloud is expected on Wednesday with afternoon freezing levels around 1500m and light alpine wind. A storm system is currently forecast to bring 20-30mm of precipitation to the region Wednesday overnight and Thursday with freezing levels climbing to around 2000m.
Avalanche Summary
On Sunday, natural and human-triggered storm slab avalanches up to size 2 were reported, as well as loose wet avalanches below around 2000m. Several natural storm slabs failed on the late-February weak layer. These were above 2100m and were primarily on northwest through east aspects. A skier triggered a size 1.5 slab on a convexity on a northwest aspect at 1950m which failed on the late-Feb layer down 30-50cm. A skier kicked a cornice which triggered a size 2 slab on a northeast aspect at 2200m which also failed on the late-Feb layer down 40-70cm.
Snowpack Summary
A widespread rain crust is expected to extend into the alpine. The late-February surface hoar layer is now typically down 40-70cm and may still be reactive. This surface hoar layer was widespread above 1700m except on south aspects where the interface was cooked by the sun and now exists as a buried sun crust. Significant wind transport has been noted so expect to find winds slabs in exposed lee terrain at higher elevations. 80-100cm below the surface you will likely find the mid-February crust/facet/surface hoar layer but this layer is now considered inactive.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.