Regions
Kootenay Boundary.
Storm slabs continue to be a concern. Wide fracture propagations are possible where the storm snow is sitting on a weak buried layer of surface hoar.
Confidence
Moderate - Freezing levels are uncertain on Monday
Weather Forecast
Freezing level dropping down close to valley bottoms overnight with continued light precipitation. Light precipitation and cloudy skies on Monday combined with moderate southerly winds and freezing levels climbing up to about 1700 metres. A spring diurnal freeze/thaw cycle setting up for Tuesday and Wednesday with freezing levels dropping to valley bottoms overnight and then rising up to 1500 metres during the day. The next major storm pulse developing on Wednesday night.
Avalanche Summary
Loose wet avalanches and moist storm snow avalanches were reported on Sunday. Natural avalanches were reported up to size 2.5 on Saturday. Skier accidental, remotely triggered slab avalanches, and natural avalanches up to size 2.0 were reported on Friday. Explosives also released cornices up to size 3.0. On Thursday, a size 1.5 storm slab was ski cut on a northwest aspects at 2050m. This slab failed on the late-February surface hoar layer down 30-50cm. Numerous small ski cut avalanche were also reported to be failing on this layer through the region.
Snowpack Summary
Forecast rain and high freezing levels may rapidly increase the likelihood of triggering storm slabs and persistent weak layers. New snow and wind has added to the 30-50cm of recent storm snow that overlies a layer of well-developed surface hoar (up to size 20mm) which is very reactive to human triggers. This layer is 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 deeper, more destructive slabs in exposed lee terrain. 80-100cm below the surface you will likely find the mid-February crust/facet/surface hoar layer. Although this layer has become less likely to trigger, avalanches failing at this interface could be large and destructive.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.