Regions
Kootenay Boundary.
Recent snowpack and avalanche observations from the Rossland Range indicate that the Danger Rating below treeline is CONSIDERABLE in that area. The Special Public Avalanche Warning is extended through the weekend.
Confidence
Fair - Intensity of incoming weather systems is uncertain on Sunday
Weather Forecast
A pacific frontal system will enter the region on Sunday. Moderate to heavy snowfall is expected by Sunday evening and should continue until Monday night. Mainly light flurries are forecast for Tuesday. Winds should remain strong to extreme from the west throughout the forecast period. Weather models are currently disagreeing on forecast temperatures. On Sunday confidence is good, and freezing levels should remain at valley bottom. Monday and Tuesday is where uncertainty lies with some models calling for freezing levels rising to 1250m. We should have a better handle on this by Sunday.
Avalanche Summary
In general, persistent slab avalanches to size 2 continue to occur in the Kootenay Boundary region. On Saturday, skiers accidentally triggered size 1 slabs around treeline in the Selkirks and the Monashees. Both avalanches failed on the mid-December layers.The mid-December layer remains the most concerning, and with new snow in the forecast avalanche danger will be on the rise at ALL elevations.
Snowpack Summary
Light amounts of low density snow overlie a variety of snow surfaces. Wind exposed slopes are showing firm wind pressing, or a scoured exposed crust, while sheltered locations have up to 35 cm of light, low density, faceted snow above recently formed surface hoar. Stiff and reactive wind slabs exist primarily on southerly aspects. Up to 80 cm below the surface, you'll likely find a touchy weak layer of surface hoar sitting on a thick rain crust. This widespread persistent weakness was buried mid-December and continues to produce whumpfing and sudden planar characteristics in snowpack tests. Although high elevation slopes may not have the rain crust, they are still reported to have touchy buried surface hoar. At the base of the snowpack, a crust/facet combo appears to have gone dormant for the time being.
Problems
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.
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.