Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
A storm passes to the South of the region Friday night into Saturday, but the Purcells will be just on the edge of the system. As a result, only a few cm of snow are expected. Winds will be out of the SW Saturday at Moderate speeds, gusting strong. The freezing level is expected to remain near 1000m.Skies will remain overcast Sunday as a weak upper trough passes over the region. Freezing levels remain constant near 1000m and winds should be light out of the W, SW.
Avalanche Summary
A couple of size 3.0 avalanches were reported from the northern Purcells, one that stepped down to the ground around midway down the path. The other avalanche was on a cross loaded slope at about 2100 metres. These were reported as recent, but I am not sure of the occurrence date. No new avalanche observations were reported Thursday.
Snowpack Summary
Widespread surface hoar has been buried by a couple of cm of new snow in most of the region. A melt-freeze crust has developed on southerly aspects at all elevations. North and east aspects continue to have dry snow and some surface sloughing in steep terrain. Basal facets have not been reactive, but operators continue to monitor this layer in tests. Triggering this deep persistent weak layer is unlikely, but shallow snowpack areas or shallow weak areas adjacent to deeper wind loaded slopes are suspect locations.
Problems
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.
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.