SW Wind and new snow have formed thin sensitive windslab at and above treeline.
Weather Forecast
Alpine temps will remain cool with freezing level of 1200m. Scattered flurries will bring another 4cm and moderate to strong SW winds will redistribute the storm snow onto lee slopes up high. Light precipitation, moderate west winds and cool temps expected to mid-week.
Snowpack Summary
Wind effected snow at and above treeline, with windslab on lee features. Near surface crusts will be lurking under 10cm+/- snow below 1700m. Feb 27th layer down 70cm has been most reactive on solar slopes. Feb 10th interface down 120cm+/- may react in a step down type slide where the extra load wakes it up. Cornices are large, fragile and failing.
Avalanche Summary
Three skier accidental thin surface slabs were triggered in the Balu Pass area yesterday on easterly aspect. These slides were composed of the surface slab, 10-15cm deep, 50-60m wide and ran 50m+. 4 slides in the size 1.5 range observed in the highway corridor.
Confidence
Due to the number of field observations
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.