Regions
Northwest Coastal.
New snow and strong winds are expected to continue adding to the widespread wind slab problem.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The first of two cold fronts is expected to bring 10-15 cm snow on Friday, with strong southerly winds and the freezing level rising to around 1200 m. There is a lull on Saturday before the second front brings around 15 cm and more strong winds on Sunday.
Avalanche Summary
Size 1-2 wind slabs were triggered naturally and by skiers on Wednesday, mostly at alpine and treeline elevations.
Snowpack Summary
Recent strong winds have created wind slabs on a variety of slopes at alpine and treeline elevations. Incoming snow will bury a thin sun crust on sunny aspects and surface hoar in isolated sheltered and shady locations. 40-100 cm of snow sits above a melt freeze crust buried around February 12th. This crust extends up to about 2000 m. Although the snow above is bonding well to this crust in most places, recent snow pit tests northwest of Terrace produced failures on or in facets just below this layer under moderate to hard loads. Below this, a layer of surface hoar buried late in January remains a concern in thin snowpack areas in the east and north of the region. The snowpack in these areas may also sit on a weak base of facets near the ground. Below treeline, the snowpack depth is lean to non-existent in the south. In the north, the below treeline snowpack is generally considered strong.
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.