Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain on Thursday
Weather Forecast
Thursday: Cloudy with some sunny breaks. Alpine temperatures -2. Ridgetop winds light-moderate from the South. Freezing levels rising to 1600 m.Friday: Snow amounts up to 8 cm. Alpine temperatures near -4. Freezing levels 1000 m.Saturday: Mainly cloudy with isolated flurries, alpine temperatures -9, light westerly winds.
Avalanche Summary
The deep persistent slab problem continues to be reactive up to size 2 with larger triggers such as explosives. Rider triggering is possible especially in shallow snowpack areas like rocky outcrops or near small trees. Additionally on Monday a natural size 2 avalanche was reportedly seen from a NE aspect at 2300 m.
Snowpack Summary
Up to 20 cm of new storm snow covers stiff, dense wind slabs in exposed lee terrain at and above treeline. Average snowpack depths at treeline elevations are 100-130 cm. In the upper 80 cm of the snowpack a couple persistent weak layers exist, comprising of surface hoar and a facet/crust combo. This interface has produced variable results with snowpack tests, and operators are keeping a close eye on them as the load above increases and/or a slab develops.A bigger concern, especially in the Northern part of the region where the snowpack is thinner and more variable is weak faceted and depth hoar crystals combined with a crust from early October. This is now down around 80-120 cm. This deep persistent weakness may be stubborn to trigger, especially in deeper snowpack areas, but the sensitivity to triggers likely increases in shallower locations, especially on steep, convex, north-facing slopes.
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.