New snow, strong winds and rising temperatures make a good recipe for rising avalanche danger over the next few days.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
Expect light to moderate snow from Saturday to Monday. Temperatures rise towards 0 at 1500m by Saturday. Winds are expected to be moderate to strong from the west to south-west throughout the period.
Avalanche Summary
Reports suggest that recent new snow is failing on the buried surface hoar and sluffing fast in steep terrain. In areas affected by wind, slabs may have formed above this weak interface. Explosives control on Thursday produced two size 2 avalanches in steep rocky alpine terrain. Several bombs produced no results.
Snowpack Summary
Storm snow is expected to bond poorly to a layer of large surface hoar. Below around 2100m, this surface hoar sits on a hard rain crust. Above 2100m the surface hoar sits on well settled and faceted snow. A thick rain crust with facets from early November is buried over 1 m down and may still be reactive in isolated areas.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.