3 cornice collapses that triggerred sz3 avalanches on underlying slopes were observed on Thursday. Use caution around these beasts. Also, when the sun comes out, stability decreases on solar aspects so pay attention to whats overhead.
Confidence
High - Timing or intensity of solar radiation is uncertain on Friday
Weather Forecast
The freezing level is forecast to be around 1600m tomorrow with alpine temperatures around -5C. The sun will likely come out so plan for some decreasing stability on Solar aspects later in the day.
Avalanche Summary
There was a few new sz 3 avalanches occurring on eastern aspects that were likely caused by cornice collapses overnight. One of these avalanches (on Snow Peak) was over 400m wide and up to 1m deep.
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.