Regions
Kootenay Boundary.
New snow and wind will likely build reactive storm slabs. Storm slabs may have the potential to trigger deeper weakness in shallow snowpack areas. Conservative terrain selection is key for the weekend.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The weather pattern has finally shifted as a surface low moves onto the Interior bringing new snow through the weekend. Saturday: Snow amounts 10-20 cm with light- gusting strong southwest winds. Alpine temperatures near -4 and freezing levels 1200 m. Sunday: Snow amounts up to 20 cm with strong southwest winds. Alpine temperatures -3 and freezing levels 1300 m.Monday: Snow accumulations up to 20 cm with light southwest winds. Alpine temperatures near -3.
Avalanche Summary
No new avalanche observations were reported on Thursday. New building storm slabs will likely have a poor bond to the old snow surfaces and be reactive through the weekend, potentially stepping down and initiating deep persistent slabs.
Snowpack Summary
New snow has buried a variety of old snow surfaces including stiff wind slab or wind effected snow at upper elevations, sun crust on steep southerly slopes and surface hoar in sheltered areas. Below the surface, 50-65 cm of settled snow now sits above an interface that was buried in mid-January. The interface is composed of weak facets, surface hoar, and/or sun crusts and the strength of the bond is reportedly variable. Recent snowpack tests have shown sudden results on that interface. Areas with a shallower snowpack (less than 150 cm) have a generally weak snowpack structure with sugary facets near the ground. This includes shallow alpine slopes and most of the Rossland range. These deeper weaknesses warrant monitoring and create a complicating picture. It may be a low probability that you would trigger an avalanche that failed on these basal facets, however; the consequences could be detrimental. These layers may be unreactive but they could reawaken with more snow load.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.