Regions
Northwest Coastal.
Confidence
Fair - Due to limited field observations
Weather Forecast
Wednesday: Moderate W winds. Alpine temp -7. Light snow. Thursday: Strong W winds. Alpine temp -7. Moderate snow (locally heavy).Friday: Light S winds. Alpine temp -7. Moderate to heavy snow.
Avalanche Summary
Large natural avalanches were heard across the valley from Shames on Tuesday. On Monday, explosives triggered several size 1.5-2.5 slabs on wind-loaded slopes north of Stewart, one of which ran on facets at the ground.
Snowpack Summary
Warm temperatures on Tuesday led to upside-down storm snow (dense snow over lighter snow) and rain at low elevations. Recent storm snow has been redistributed by very strong winds, creating wind slabs which may now be buried on a variety of slopes. The mid-pack is generally well-settled. A November facet/crust layer can be found near the base of the snowpack. Sporadic releases are still occurring on this layer with a heavy trigger. Above about 1000 m, the snowpack is 150-250 cm deep. Below about 1000 m, snowpack depths peter out pretty quickly.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.