Slab formation remains the critical factor for avalanche danger under current conditions. The best and safest riding will be in soft, unconsolidated snow.
Weather Forecast
Sunday: Mainly sunny. Light northwest winds. Alpine temperatures around -14.Monday: A mix of sun and cloud. Light north winds. Alpine temperatures around -20.Tuesday: A mix of sun and cloud. Light southwest winds. Alpine temperatures around -19.
Avalanche Summary
Reports from Friday included one skier-triggered Size 2 persistent slab avalanche from a steep, rocky feature on a west aspect at 2100m in the Monashees. The late November crust was indicated as its failure plane. Reports from the previous few days included several natural storm and wind slab avalanches to size 2.5 in the alpine and tree line. There were also a few reports of skier accidental and remote (triggered from a distance) avalanches from size 1.5-2 below tree line. These avalanches released at the December 15 interface. Persistent slab avalanche danger can be expected to persist in areas where our recent snow consolidates into a slab above the December 15 interface. In areas where new snow has not yet consolidated into a slab, expect continued potential for triggering loose dry avalanches in steep terrain.
Snowpack Summary
Last week's stormy weather brought 40-60cm of new snow to the region. Cold temperatures since the storm have generally slowed consolidation of the new snow, with the exception of wind-affected areas. The new snow lies over a wide variety of old surfaces, including large surface hoar (weak, feather-like crystals), hard crusts formed by sun or wind, and sugary facets. The bond at this old snow interface is of critical importance in areas where the overlying snow has consolidated into a slab. The most concerning areas areas will be those that have seen previous surface hoar development, such as sheltered areas at and below tree line and sheltered northerly aspects in the alpine.A crust which was formed by rain in late November is another major feature in the snowpack and is down approximately 80-110cm at treeline elevations. Although an isolated incident, one avalanche report from Friday suggests this layer can be coaxed into reacting in steep, variable snowpack areas.
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.