Regions
Kootenay Boundary.
A weak surface hoar layer down 40-70 cm is still reactive and should still be treated with extra respect.Lingering wind slabs are expected to remain reactive to human-triggering on Wednesday at higher elevations.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain on Thursday
Weather Forecast
Mostly cloudy conditions are for Wednesday with the possibility of light flurries in the morning. Freezing levels are expected to be around 1000m overnight and 1600m in the afternoon. Alpine winds are forecast to be light from the southwest. A storm system is expected to reach the region Wednesday night and 20-30mm of precipitation can be expected by Thursday afternoon. Alpine winds are expected to be strong from the southwest and freezing levels are forecast to climb to around 2000m during the storm. A mix of sun and cloud is currently expected for Friday.
Avalanche Summary
On Monday, a skier triggered a size 2.5 persistent slab avalanche on an east aspect at 2250m which released on the late-Feb surface hoar layer down 20-60cm. Explosive triggered five size 2-2.5 persistent avalanches. There were on north and east aspects between 2000 and 2200m. 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 few centimeters of new snow sits over a widespread rain crust which 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
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.
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.