Confidence
Fair - Due to limited field observations
Weather Forecast
Sunday: Expect skies to clear over the course of the day, with winds turning northerly but remaining light. Temperatures could reach -10. Monday: Winds turn westerly but remain light under continued clear skies. Tuesday: Expect clouds to build and flurries to begin late in the day under southwesterly winds. The western slopes will likely see higher accumulations, up to 10cm.
Avalanche Summary
As folks take advantage of the clear weather to get further afield we have reports of old avalanches that released on the persistent weakness deep in the snowpack. The most recent events have been isolated to small, loose sluffs on steep south facing terrain associated with the recent daytime warming.
Snowpack Summary
Some areas have seen a trace of new snow (less than 5cm), but beyond this the region has seen little change. Surface hoar continues to grow in sheltered locations and the cold temperatures are penetrating the upper snowpack to promote near surface facetting. There is some sun crust formation on steep south through west aspects. Hard windslabs linger in the alpine and open treeline locations but are softening due to the facetting phenomena. Some areas have a rain-crust below treeline from the 28th of November that has been buried by about 20 cms of snow. This rain-crust may be developing facets, and could become a layer of interest after it is buried by more of a load.The early November surface hoar remains a layer of concern. It is buried 100-150 cms and stability tests show that this layer is getting harder to trigger. However, if an avalanche does release on this layer, it is likely to be very large and destructive.
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.
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.