Fresh snow, forecast solar radiation and a complex snowpack means this is no time to be pushing into steep terrain. Conservative slope selection is critical to safe mountain travel.
Confidence
Fair - Timing or intensity of solar radiation is uncertain on Monday
Weather Forecast
Overview: A generally dry ridge of high pressure will develop on Monday and Tuesday with the passing of Sunday's frontal system. Another pulse will bring moisture to the region on Wednesday.Overnight Sunday: Up to 20cm of snow / Moderate to strong westerly winds / Freezing level at about 1500mMonday: Light flurries with a mix of sun and clouds / Light to moderate westerly winds with strong gusts / Freezing level at 1500mTuesday: Mix of sun and cloud / Light northwesterly winds with strong gusts / Freezing level at 1500mWednesday: Flurries / Moderate westerly winds / Freezing level at 1500m
Avalanche Summary
Avalanche observations were extremely limited on Sunday due to inclement weather. With Sunday's storm, I expect avalanche activity to include a significant round of storm slab activity as well as the possibility of destructive persistent slab activity. Persistent weaknesses still have the potential to react as wet slab avalanches at lower elevations where rain fell.
Snowpack Summary
As of Sunday morning up to 30cm of new snow had fallen and was blown by strong winds into much deeper deposits in lee terrain. Rain below about 1700m continued to saturate the snowpack. 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 areas the crust seems more specific to previously sun-exposed slopes. More precipitation and wind forecast for Sunday night will add to this developing storm slab. 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. Triggering will become more likely with forecast clearing and solar radiation.Cornices have also become large and potentially 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.
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.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.