Regions
Northwest Coastal.
Avalanche danger is one step higher in the north, where the recent storm dropped more snow.
Confidence
Moderate - Timing of incoming weather systems is uncertain
Weather Forecast
Expect a cloudy lull in the weather on Saturday before a front brings around 10-15 cm snow on Sunday. The freezing level is expected to be around 1000 m during the front, with strong southerly winds. Snowfall and winds ease on Monday.
Avalanche Summary
A cycle of naturally-triggered large wind slabs was observed on slopes lee to the south around Bear Pass on Thursday. Explosives also triggered size 1-2 storm slabs and wind slabs. Size 1-2 wind slabs were triggered naturally and by skiers on Wednesday, mostly at alpine and treeline elevations.
Snowpack Summary
Recent snow has been heaviest in the north of the region, creating storm slabs. These sit above old wind slabs, scoured surfaces, a thin sun crust on sunny aspects and surface hoar in isolated sheltered and shady locations. Previous strong southerly and outflow winds created widespread wind slabs on a variety of slopes at alpine and treeline elevations. These may now be buried and hard to spot. A hard crust buried around February 12th, down about 50-80 cm, extends up to about 2000 m. A layer of surface hoar buried late in January remains a lingering concern. Shallow snowpack areas may also have a weak base of facets near the ground.
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.