Caution if the sun comes out - avoid steep sunny slopes where the snow will lose cohesion.
Confidence
Low - Due to the number of field observations
Weather Forecast
THURSDAY: Mix of sun and cloud with the chance of a flurry. Freezing level at valley floor. Light winds.FRIDAY: Mix of sun and cloud. Freezing level at valley floor. Light winds.SATURDAY: Mix of sun and cloud. Freezing level at valley floor. Light winds.
Avalanche Summary
It's been fairly quiet the last couple of days, with only reports of explosives triggering one size 2 wind slab. On Monday, large (size 2) wind slab avalanches were triggered by skier and explosive activity, 30 to 50 cm deep. A deep persistent slab was also noted in the region, likely releasing on one of the layers described in the snowpack discussion.It is still possible to trigger a wind slab with the weight of a person. If the sun is shining, avoid exposure to steep solar aspects where loose wet avalanche activity is possible.
Snowpack Summary
You are likely to find variable surfaces in open terrain after recent strong winds took out their fury on the upper snowpack. Fragile cornices and hard and soft wind slabs can be found on many alpine and treeline slopes. Ongoing cold temperatures are helping to break down and soften these.A crust/surface hoar interface is about 40-60 cm down, but little is known about its sensitivity and distribution. The lower snowpack in this region is weak with two primary concerns:1) A widespread weak layer from mid-December composed of facets, crusts, and surface hoar that is 100-150 cm deep.2) A rain crust with sugary facets buried in late-November near the bottom of the snowpack.Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread.
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.