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 Thursday
Weather Forecast
Wednesday night and Thursday: 10-20cm of snow / Moderate west-northwesterly winds / Freezing level at 1000mFriday: Light snowfall / Light to moderate northwest winds / Freezing level at surfaceSaturday: Mix of sun and cloud / Light northwesterly winds / Freezing level at surface
Avalanche Summary
In recent days avalanche observations have been very limited. I expect more storm/wind slab activity in response to weather forecast for Wednesday evening.
Snowpack Summary
Up to 55cm of recent storm snow has been redistributed by strong winds into deeper deposits in lee terrain. Recent snowpack tests suggest there are still likely weaknesses near the base of the storm snow. The recent accumulations overlie hard rain crusts which exist on all aspects below 2000m and on solar aspects in the alpine. North of Sparwood and in the Crow's Nest Pass area the buried crust seems more specific to previously sun-exposed slopes. Below 1700m rain over the weekend saturated the snowpack, and old surfaces may now exist as a hard refrozen crust where temperatures have dipped below freezing.The deep facet/crust persistent weakness buried at the beginning of February, now down up to 150cm, is still producing sudden results in snowpack tests. I would be very leery of any slopes that have not already avalanched as any activity at this interface would be large and destructive. Likely 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
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.
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.