Confidence
Fair - Freezing levels are uncertain for the entire period
Weather Forecast
A firmly embedded ridge of high pressure will continue to dominate the region bringing clear skies and light southerly winds throughout the forecast period. An inversion with above freezing alpine temperatures will persist on Sunday, but will give way to a gradual cooling pattern forecast for Monday and Tuesday.
Avalanche Summary
In the Bull River area on Saturday widespread natural activity to size 3 was reported on sun-exposed aspects in the alpine. On Friday, a size 3 natural slab avalanche was reported on sun-exposed alpine feature. This was thought to have ran on basal facets. In the neighboring Lizard range numerous deep releases to size 3.5 were reported on facets that formed in October. The same snowpack structure exists in many parts of the South Rockies region.
Snowpack Summary
Storm snow from the last few weeks seems, for the most part, to be fairly well settled. In the mid snowpack sits the mid-December surface hoar layer. Lately this layer has been less of a concern. At the base of the snowpack basal facets and depth hoar seem fairly widespread in the region. The big story for the weekend has been warming at higher elevations due to an inversion and solar heating. Failing cornices, loose wet snow avalanches on sun-exposed slopes and isolated deep releases on basal facets have been the big things to watch for. In Elk Valley North and the Crowsnest, the average snowpack depth at treeline is 150 cms. Elk Valley S and the Flathead the snowpack depth is closer to 2 m.
Problems
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
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.