Small fresh wind slabs reactive to human triggers are expected to form on lee features below ridgetops on Friday.
Weather Forecast
FRIDAY: Cloudy with flurries; 5-10 cm of new snow / Moderate to strong southwesterly ridgetop winds / Freezing level around 1500 m.SATURDAY: Mostly sunny / Light southwesterly ridgetop winds / Freezing level rising to around 1800 m.SUNDAY: Mostly sunny / Light southwesterly ridgetop winds / Freezing level rising to around 2000 m.
Avalanche Summary
Numerous loose wet avalanches to size 1.5 were reported on Wednesday. Explosive control work northwest of Elkford on Tuesday produced numerous size 3 persistent slab avalanches failing on facets near the base of the snowpack. The most notable results were on steep, rocky north aspects, and lower angled west aspects.
Snowpack Summary
Up to 10 cm of new snow on Thursday overlies sun crusts on solar aspects with generally better riding conditions on north and east aspects. The lower snowpack is generally weak with the primary concern being a combination of crusts and facets near the bottom of the snowpack that are widespread. The primary concern looking ahead towards the weekend and early next week is the potential of these deeper persistent weak layers becoming active by rapid warming of the snowpack through rising freezing levels and intense solar radiation.
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.