New snow, strong winds and rising temperatures make a good recipe for rising avalanche danger.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
Light to locally moderate snow is expected in pulses from Sunday to Tuesday. The heaviest snowfall is expected overnight Saturday/Sunday (15-40 cm) and should be accompanied by moderate to strong westerly winds. Freezing levels are expected to be around 1500m on Sunday, gradually dropping to near 800m by Tuesday.
Avalanche Summary
In areas which have already received 30 cm or more of storm snow above the surface hoar/crust interface, skiers were easily triggering slabs to size 1.5 on Friday (including one remote trigger with a partial burial). Other parts of the region may be slightly below the 'tipping point' today, but should have reached it by Sunday. I expect very touchy conditions on Sunday, with natural activity likely overnight Saturday and skier triggering of storm slabs likely on Sunday.
Snowpack Summary
Storm snow and wind slabs are building up. These are bonding poorly to a layer of large surface hoar crystals. 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.