A deeply buried weak layer is still producing large destructive avalanches in isolated areas and may be remotely triggered from a distance. Use extra caution around steep, unsupported alpine terrain.
Confidence
Fair - Due to the number of field observations
Weather Forecast
High pressure persists over the interior for the forecast period. On Tuesday, expect a mix of sun and cloud, treeline temperatures around -12, and light alpine winds. Conditions should be similar on Wednesday and Thursday with a mix of sun and cloud, treeline temperatures around -10, and light alpine winds.
Avalanche Summary
No new avalanches were reported at publish time on Monday. On Sunday, snowmobiles remotely triggered a persistent slab with a crown depth around 1.5m in the Allan Creek area. On Saturday, two size 2 remotely triggered persistent slab avalanches were reported. These were triggered from 250m away and released 80-100cm down on the old rain crust from early November. These occurred around 2000-2200m elevation on NW aspects.
Snowpack Summary
A surface crust exists up to around 1800m elevation. Above this elevation is dry storm snow which is settling out and faceting. A new layer of surface hoar is currently forming on the snow surface. In exposed alpine terrain, strong southerly winds last week may have resulted in variable distribution of the surface snow and the formation of wind slabs. The early November crust/facet layer is down around 1 m in the south of the region, probably less in the north. We received reports that this deep weak layer has resulted in remotely triggered avalanches over the weekend.
Problems
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.
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.