The recent storm snow is expected to be very touchy on Tuesday, especially in wind loaded terrain. Conservative terrain selection remains critical.If the sun comes out in the afternoon, avoid all sun exposed slopes.
Confidence
Low - Due to the number of field observations on Monday
Weather Forecast
Lingering flurries are possible on Tuesday morning and a mix of sun and cloud is expected for Tuesday afternoon. Alpine wind is forecast to be moderate from the west and treeline temperatures are expected to be around -15C. A mix of sun and cloud is expected on Wednesday with moderate alpine wind from the west and treeline temperatures around -15C. The next storm system is currently forecast to arrive on Wednesday night and 5-15 cm of snowfall is forecast for Thursday with strong southwest wind and freezing levels climbing to around 1500 m elevation.
Avalanche Summary
An early report from Monday includes numerous skier triggered storm slab avalanches size 1-1.5. Explosives also triggered storm slabs up to size 2.5. These slabs were typically around 30 cm thick. One of these storm slab avalanches stepped down to the basal weakness resulting in a slab that was up to 150 cm thick. On Sunday, explosives and skiers were triggering storm slabs up to size 2 with typical slab thickness of 30-40 cm. The recent storm snow is expected to remain very touchy on Tuesday, especially where it has been redistributed by the wind. Storm slab avalanches also have the potential to step down to the basal weakness which would drastically increase the size and destructive potential of a resulting avalanche.
Snowpack Summary
Up to 90 cm of new low density storm snow has accumulated over the weekend. Strong shifting winds have redistributed the new snow in exposed terrain forming very touchy wind slabs. The new snow overlies a highly variable old surface which may include wind affected surfaces, facets, and/or a rain crust below around 1500 m. Recent reports suggest a poor bond between the new snow and the old surface. In deeper areas, the snowpack appears to be well settled with isolated concerns about the mid-December facet layer which was buried 50-100 cm deep prior to the weekend storm. In shallow snowpack areas and lower elevations, the snowpack is weak and faceted. For instance, in the Elk Valley north area near Crown Mountain last week the height of snow was 90 cm with foot penetration of 80 cm; or almost to ground. In these areas, the wind has formed isolated hard slabs above weak facets and created the potential for large persistent slab avalanches.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.