Colder temperatures have improved conditions within the upper snowpack, however lingering deep persistent instabilities remain a concern in isolated areas.
Confidence
Good - Due to the quality of field observations
Weather Forecast
Freezing levels are expected to drop to valley bottoms tonight and light accumulations of 2-5cm are likely to fall early Saturday morning. Saturday is expected to be overcast with moderate variable winds and a high around -9 at treeline. Sunday should remain overcast with the possibility of very light accumulations. Monday we may see another system bring 5-10cm of snow and warmer temperatures.
Avalanche Summary
No new avalanches have been reported. On Wednesday a size 2 avalanche was accidentally triggered on an east aspect in the alpine by a sledder near Racehorse Pass (Crowsnest) on the December PWL.
Snowpack Summary
Recent warm sunny conditions and high freezing levels have created a melt freeze cycle in the upper levels of the snowpack. These warm conditions have decimated the lower elevation snowpack and the threshold for avalanches has risen to approximately 1600m, potentially higher on solar aspects. In most areas of the region, a new crust has formed on the surface of the snowpack up to 1800m and up to all elevations on solar aspects. The mid-December crust/facet/surface hoar layer is down 40-80cm and remains reactive in isolated areas, especially where a slab of stiffer snow has consolidated above it. This layer has proven easier to trigger from shallow and rocky areas in the alpine and treeline.
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.