Wind slab conditions are highly variable. A natural avalanche cycle seems to be tapering off, but conditions are ripe for human-triggering. Choose conservative terrain as full depth avalanches are possible due to lingering deep instabilities.
Weather Forecast
Thursday will bring cloudy skies with sunny periods and isolated flurries. Alpine temperatures will reach a high of -8 °C. Ridge-top winds will be out of the west at 25 km/h gusting to 50 km/h. A clearing and warming trend is expected for the weekend with freezing levels rising significantly by Saturday.
Avalanche Summary
A few very small loose dry avalanches from steep Alpine terrain on N and E aspects. Further evidence of a recent (past 48+ hours) natural slab avalanche cycle up to size 3.0 on North, East and South aspects in the Alpine. These slabs vary in thickness from 60 to 100cm and some exhibited significant propagation. Some slides have also stepped to ground after originally initiating on a weakness in the mid-snowpack.
Snowpack Summary
Variable wind effect in lee and cross-loaded features in the Alpine and isolated areas at Treeline. Some reverse wind-loading due to recent northerly winds. Numerous buried crusts are found on solar aspects which were producing generally moderate shears down 32 and 50cm in snowpack stability tests today at 2300m. Cornices continue to grow with several failures observed over the past several days.
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.
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.
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.