Regions
Banff Yoho Kootenay.
The first major warm up of the spring season is occurring right now accompanied by strong winds. This is a time to travel cautiously as we expect avalanche activity to increase and we may start to see failures on our deep persistent weak layers.
Weather Forecast
Strong SW winds, 5-15cms of snow, and rising freezing levels up to 2500m are forecast for Tuesday. Wednesday should see freezing levels drop back down to valley bottom with continued strong winds, cloudy weather and snow flurries. Thursday is a mix of sun and cloud and daytime freezing levels up to 2100m.
Snowpack Summary
Moist snow to 2000m on all aspects and to ridge top on solar aspects. Thin wind slabs in open areas. Western areas such as Emerald and Field have a deep and stable snowpack. The Lake Louise, Hwy 93 N, & Sunshine areas have a weaker snowpack and we are still getting easy to moderate sudden collapse results on the basal depth hoar in some areas.
Avalanche Summary
Loose wet sluffs observed in steep terrain on all aspects below 2000m and on solar aspects to ridge tops. Natural cornice failures have occurred in the last 48hrs creating slab avalanches to size 2. Kananaskis had a skier accidental yesterday in a thin snowpack area failing on the basal facets. We expect avalanche activity to increase tomorrow.
Confidence
Intensity of incoming weather systems is uncertain on Tuesday
Problems
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.