Regions
Kootenay Boundary.
Wind slabs are the primary concern and may be reactive to rider triggers. In shallow snowpack areas wind slabs could step down to deeper weak layers initiating a large and destructive avalanche.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The pattern finally changes as the cold arctic high shifts, allowing pacific low pressure systems to invade the Interior through the forecast period.Friday: Snow amounts 5-10 cm with light winds from the South. Alpine temperatures near -6 and freezing levels 700 m.Saturday: Snow amounts 10-20 cm with ridgetop winds generally light, gusting strong from the southwest. Alpine temperatures near -5 with freezing levels rising to 1200 m.Sunday: Snow amounts 15-25 cm with ridgetop winds light-strong from the southwest. Alpine temperatures near -2 and freezing levels rising to 1300 m.
Avalanche Summary
On Wednesday surface sluffing and solar induced loose dry avalanches up to size 1.5 were reported. Depending on snow amounts for Friday you could see loose dry sluffing from steeper terrain features and potentially new wind slab development. The new snow will likely have a poor bond to the old snow surfaces. Expect buried wind slabs to linger on lee and crossloaded features at higher elevations.
Snowpack Summary
In exposed areas at treeline and in the alpine, the surface snow consists of stiff wind slab or wind effected snow. Adding to the mix you may see 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 facets, surface hoar, and/or sun crusts and the strength is reportedly variable. Recent snowpack tests have shown sudden results on that interface. Areas with thin snowpacks (e.g. 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. This makes for tricky especially decision making. These layers may be unreactive or even sit dormant now with this stable weather pattern but they could reawaken with a change.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.