Regions
Kootenay Boundary.
Forecast snow amounts vary through the region. If your local riding area receives less then 25 cm of new snow please consider the danger rating to be CONSIDERABLE on Wednesday.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Wednesday
Weather Forecast
Wednesday: Snow amounts 10-15 cm with alpine temperatures near -4. Ridgetop winds moderate from the west and freezing levels near 1500 m.Thursday: Snow amounts up to 30 cm accompanied by strong west winds. Freezing levels near 1500 m. Friday: mix of sun and cloud with freezing levels falling to valley bottom. Alpine temperatures near -12.
Avalanche Summary
Avalanche activity is ongoing through the region. On Monday, several natural storm slab avalanches and skier triggered avalanches up to size 2.5 were reported. These avalanches were mostly seen from NNE-E aspects above 1900 m. There was one deep persistent slab that pulled as a natural size 3.5. It ran full path to a historical run-out through 15 m worth of mature timber. This was reported from a east aspect at 2100-2300 m, running 900 m in length and up to 400 m wide. Looking forward with forecast snow and wind, expect newly formed storm slabs and the persistent slabs beneath them to remain reactive to human triggers with the potential for very large and destructive avalanches.
Snowpack Summary
Recent storm snow totals vary from 25-50 cm and the winds created reactive wind slabs at tree line and above. Forecast storm snow amounts vary but the region will see significant amounts by Thursday, adding stress to the underlying and very complex snowpack. Deeper in the snowpack, surface hoar and/or a crust from mid-January is buried beneath all the storm snow at 90-120cm deep. This interface has been reactive and this interface remains a concern. Below this layer lies a second crust/surface hoar interface buried early-January that is now 120-140 cm deep. Recent avalanches have stepped down to this layer and it should remain on your radar.The mid-December surface hoar layer is buried 130-170 cm below the surface. This layer has continued to produce step down releases and "sudden" test results. It is most pronounced at tree line and below treeline and has remains reactive especially in steeper, unsupported convex terrain features.
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.