It is still possible to trigger large persistent slab avalanches throughout most of the region. Dealing with this type of problem requires discipline to stick to conservative decision making, even when no obvious signs of instability are observed.
Confidence
Fair - Forecast snowfall amounts are uncertain
Weather Forecast
Friday: Cloudy with isolated flurries. Winds light southwest. Freezing level rising to 1500m.Saturday: Light to locally moderate snowfall overnight Friday into Saturday. Freezing level 1600m. Winds light southwest.Sunday: Cloudy with scattered flurries. Freezing level rising to 1800m.
Avalanche Summary
Recent reports from the central part of the region (where the most recent snowfall was intensified) indicate natural and explosives triggered avalanches running in the alpine to size 2.5 on all aspects. These were isolated to the most recent storm snow.A size 3 accidentally skier triggered avalanche was reported last Sunday. This avalanche occurred on a steep west-facing alpine slope and stepped down to the ground (up to 2.5 m deep). One person was buried but was recovered without serious injury. On Saturday an anomalous sized 3.5 avalanche released naturally out of a SE facing feature at 2700m in the central portion of the region. Another skier triggered size 2 avalanche was reported on Tuesday. This was in the northern part of the region at 2300m on a northwest aspect, failing on facets near the base of the snowpack.
Snowpack Summary
5-40cm of new snow has fallen in the region (5-10 in the north and up to 40 in the central). This new snow is settling and likely being formed into soft wind slabs immediately lee of ridge crests.Numerous crusts can be found in the upper 60cm of the snowpack on south facing slopes. The March 15 crust/surface hoar interface is down 50-80cm. Down90-120cm below the surface you may find surface hoar and crusts buried at the beginning of March. This interface is still touchy in some areas, particularly in the north of the region. It also continues to produce sudden planar failures in compression tests.The deeper facet/crust persistent weakness buried at the beginning of February, now down 120 - 200cm, still seems to be reactive and should not be trusted. Needless to say, any avalanche at these deeper, persistent interfaces would be large and destructive. Weak basal facets exist in many areas, but without a large load, triggering is unlikely.
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.