Regions
Kootenay Boundary.
Special Avalanche Warning in effect for the interior ranges. Copy this address to view details: http://bit.ly/2nSOUyX
Weather Forecast
Friday: Cloudy with sunny periods. Alpine temperatures near -11 and freezing levels dropping to valley bottom. Ridgetop winds light from the northeast.Saturday: Sunny. Alpine temperatures near -10 and freezing levels valley bottom. Light winds from the west.Sunday: A mix of sun and cloud. Alpine temperatures -7 and freezing levels rising to 800 m.
Avalanche Summary
On Thursday, avalanche control using explosives triggered numerous loose wet avalanches up to size 2 and a significant size 3 storm slab avalanche. These were reported from SE-SW slopes above 1900 m. The snowpack is complex, it requires patience and discipline. Natural avalanche activity may spike with the first hit of sun then start to taper off through the weekend, slopes will remain primed for human triggers.
Snowpack Summary
Recent snow accumulations vary showing 10-30 cm across the region adding more load and stress to the upper snowpack. This now brings 90-140 cm of settled snow over two surface hoar/ crust layers that were formed early to mid-January. Digging deeper 160-200 cm sits the mid-December surface hoar layer and near the base of the snowpack exists a crust/ facet interface which could be triggered by a large load like a step down avalanche or cornice failure.These persistent weak layers lurk within the snowpack and continue to be reactive, producing large and destructive avalanches. The snowpack is extremely complex and requires respect and diligence at this time.
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.