Spring conditions typically means the hazard is highest during the heat of the afternoon. Cornices and loose wet sluffing are spring problems which can be expected on Saturday. Deep persistent avalanches may become possible with sustained warming.
Weather Forecast
The warm ridge of high pressure persists through the weekend. Saturday and Sunday are expected to be sunny with light alpine winds and afternoon freezing levels around 3000m. Unsettled conditions are expected for Monday with a mix of sun and cloud. Moderate southwest winds are expected in the alpine and freezing levels are expected to drop to around 2200m.
Avalanche Summary
On Thursday, explosives triggered two size 3 persistent slab avalanches north of Pemberton on southern aspect slopes at around 2100m elevation. The slabs were 40-50cm thick and were suspected to have failed on a crust from the end of February. Explosives also triggered two size 2.5 wet slab avalanches. Loose wet sluffing up to size 2.5 was also reported. On Wednesday, natural loose wet avalanches up to size 1.5 were reported. Skiers and explosives were triggering wind slabs up to size 1.5 in leeward features and on steep rolls. A couple point releases triggered slabs up to size 2.5. With warm and sunny conditions continuing, spring avalanche problems are expected to be the primary concerns. Loose wet avalanches and large cornice falls are expected throughout the forecast period. Wet slabs and deeper persistent slab avalanches may be possible while the temperatures remain high and overnight recovery is poor. Lingering wind slabs may also still be a problem on high elevation north aspects.
Snowpack Summary
Little to no overnight recovery was reported on Friday morning leaving a moist or wet snow surface on all aspects and elevations. The early-April crust layer is typically down 10-20cm and is reported to be breaking down due to the warm conditions. Prior to the warming, the recent storm snow had been shifted by strong southerly winds into wind slabs in wind-exposed terrain. These wind slabs may still be lingering in high north facing terrain. There is an old crust layer down about half a meter in the Duffey area and north of Pemberton. This layer has generally be dormant but resulted in a couple avalanches during the last major warming event and produced a couple explosive triggered avalanches on Thursday. With continued warming, this layer could wake-up and become a more widespread problem. Cornices are huge and will become weak with warming and solar radiation.
Problems
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.
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.