Regions
Kootenay Boundary.
Rising temperatures, strong winds, and increasing snow load are the perfect recipe for avalanches. Conservative terrain selection is highly recommended.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A pacific storm system is expected to reach the region on Wednesday night. 20-30cm of snowfall is expected between Wednesday night and Thursday evening. Freezing levels are expected to hover around 1500m during the storm and alpine winds should be strong from the southwest. A mix of sun and cloud is expected for Friday with freezing levels around 1000m and light alpine winds. Light snowfall is being forecast for Friday night or Saturday morning with models showing around 5cm.
Avalanche Summary
On Tuesday, a skier accidently triggered a size 1 storm slab avalanche on a northeast aspect at 2000m. The slab released within the recent storm snow down 35cm. On Monday, a skier accidently triggered a size 1 storm slab on a north aspect at 1950m elevation. The slab released within the recent storm snow down 30cm. Storm slabs may become reactive during Thursday's storm in deeper snowfall areas. In areas that receive less snowfall, wind slabs will be the primary concern. Extra caution is required where smaller avalanches have the potential to step down to deeper weak layers that may be preserved.
Snowpack Summary
Thursday's storm snow is expected to sit over recently buried surface hoar that is reported to be 5-10mm in the north of the region. Strong southwest winds will likely form new wind slabs in leeward features and stiffer old wind slabs may still be reactive in steep unsupported features. In deeper snowfall areas, a more widespread storm slab may form and could quickly become reactive. A thin rain crust is reported to be as high as 2000m and down around 20cm in the snowpack. The recently destructive early January surface layer is down 60-100cm and is most prominent on all aspects at treeline and below. It is getting harder to trigger this layer but it is still very reactive in snowpack tests suggesting that if you are able to trigger it, the layer is capable of wide propagations and large destructive avalanches. A rain crust from December can likely still be found down 100-150cm down but is generally considered inactive. Below this layer then snowpack is generally strong and well settled.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.