Regions
Banff Yoho Kootenay.
Watch the temperatures on Saturday as freezing levels are expected to rise accompanied by light winds and light snow. Human triggered avalanches likelihood will rise as the snowpack has poor structure and is in a fragile state awaiting a trigger. PJ
Weather Forecast
Westerly flow will bring light snowfall amounts and light winds for the next few days but the main criteria this weekend will be warming temperature & rising freezing levels exceeding 1800 meters by Saturday afternoon. This will be one of the most significant weather criteria and needs to be monitored closely.
Snowpack Summary
The storm snow from last week's storm is a soft slab in sheltered locations and wind scoured and hard wind slab in open terrain at tree line and above. The lower half of the snowpack is complex and poorly structured, comprised of the facets (Nov 24th) at the interface of the recent storm snow and a series of thin crusts (Nov 6th) and depth hoar.
Avalanche Summary
There has not been a great deal of natural activity observed however explosive results were reported from around the ski areas and produced slab avalanches up to size 2.5 with the slab failing on the basal facets and crusts right on the ground. These kinds avalanches are a dirty & rough ride through scree, rocks and trees & are human trigger able.
Confidence
Freezing levels are uncertain on Saturday
Problems
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.
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.