Watch the temperature and solar warming! Heat and cornices are two great ways to shake-up the snowpack over the next couple of days
Confidence
Fair - Forecast snowfall amounts are uncertain on Friday
Weather Forecast
Thursday night and Friday: Up to 20cm of snow overnight Thursday, becoming light on Friday / Light to moderate northwest winds / Freezing level at surfaceSaturday: Flurries with a mix of sun and cloud / Light to moderate northwest winds / Freezing level at surfaceSunday: Flurries with a mix of sun and cloud / Light to moderate northwest winds / Freezing level at surface
Avalanche Summary
On Wednesday a size 2 wind slab was accidentally triggered by a skier in the southeast corner of the region. The avalanche occurred on a northeast aspect at about 2600m. Although observations were limited, I expect there would have been a round of storm slab activity in response to new snow and wind on Thursday. Looking forward, continued snowfall will likely promote ongoing storm slab activity while intermittent sunshine may spark a loose wet avalanche cycle.
Snowpack Summary
At the time of publishing this bulletin up to 30cm of new snow had fallen and had been pushed by moderate to strong southwest winds into deeper deposits in exposed lee terrain. Below the new snow is a well settled storm slab which overlies a hard rain crusts. This crust exists on all aspects below 2000m and on solar aspects in the high alpine. North of Sparwood and in the Crow's Nest Pass area the buried crust seems more specific to previously sun-exposed slopes. The deep facet/crust persistent weakness buried at the beginning of February (now down up to 150cm) seems unlikely to trigger in areas where the hard, supportive near-surface crust exists. No matter where you are in the region, this weakness should stay on your radar as any activity at this interface would be large and destructive. Possible triggers include a large cornice fall, a large input in a thin snowpack area or solar warming.Cornices have also become large and unstable.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
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.