Confidence
Fair - Due to limited field observationsfor the entire period
Weather Forecast
Friday: Mostly sunny and dry with light winds. The strong temperature inversion continues with above freezing alpine temperatures and the possibility of valley cloud. Saturday: Increasing clouds and light southwest winds with light precipitation starting in the evening. The temperature inversion is expected to dissipate with freezing levels as high as 1400m. Sunday: Light snowfall, freezing levels lowering to 900m, and light to moderate southwest winds.
Avalanche Summary
There have been no recent avalanches reported. Although the likelihood of triggering deep persistent slab avalanches is low, the potential consequences are still very high.
Snowpack Summary
Basal depth hoar with an associated crust is prevalent in thin snowpack areas, and especially problematic where it is overlying summer firn. Above that, and down 1-2m, are two more crusts mixed with facets, depth hoar, and surface hoar. The overlying snow has recently settled and stiffened and the facets have started to round and strengthen, but recent compression tests in a shallow snowpack area produced moderate sudden collapse results on this deep persistent weakness. The snow surface is wind hammered in wind-exposed areas, crusty on sun-exposed slopes, and faceted powder with large surface hoar on shady sheltered slopes. A thick rain crust is down 20-40cm and extends up to treeline elevations.
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.