A week of heavy snowfall and strong winds have left large storm slabs primed for human triggering. Avoid overhead hazards and stick to mellow terrain.
Confidence
Moderate - Wind speed and direction is uncertain
Weather Forecast
SUNDAY: Light snow with up to 5 cm accumulations in the afternoon, moderate southwest winds, alpine temperatures around -10 C.MONDAY: Cloudy with isolated flurries, strong southwest winds, alpine temperatures around -12 C.TUESDAY: Cloudy with isolated flurries, strong southwest winds, alpine temperatures around -10 C.
Avalanche Summary
On Saturday, several size 2 natural storm slabs were reported in alpine terrain and explosive control and ski cutting produced size 1-1.5 avalanches at treeline and in the alpine. On Thursday, a size 2.5 deep persistent slab avalanche was reported from the Elkford-North riding area. It was from approximately 2500 m on a SE aspect. It looked to be 24 hrs old and likely failed earlier in the storm. It failed within the basal facets (deep persistent slab) and scrubbed down to rocks.Natural activity is expected to taper off, but storm slabs will remain primed for human triggering.
Snowpack Summary
Another 15 cm of new snow on Friday brings the three day total to 20-30 cm and the total from the past week to 40-80 cm. Strong southwesterly winds have redistributed the new snow onto leeward slopes, building thicker and stiffer slabs. The new snow will likely have a poor bond to the old snow interface that consists of stiff wind slabs, crusts, and facets. The mid-pack in this region is generally strong, but the bottom third of the snowpack is composed of weak facets (sugary snow crystals). Approximately 100-120 cm of settled snow sits above this weak layer of sugary, rotten facets that developed in December. This remains a concern and should be on your radar, especially with the recent loading from snow and wind.
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.