Deeply buried weak layers are lingering near the base of the snowpack. These layers are most likely to be triggered from thin or variable snowpack areas or with a large load like a cornice fall.
Weather Forecast
SUNDAY: Sunny / Light southwesterly ridgetop winds / Freezing level rising to around 2300 m.MONDAY: Sunny / Light southwesterly ridgetop winds / Freezing level rising to around 2400 m.TUESDAY: Sunny / Light southwesterly ridgetop winds / Freezing level rising to around 3000 m.
Avalanche Summary
Several human triggered wind slabs up to size 1.5 were reported on northeasterly slopes on Friday. Explosive control work northwest of Elkford on Tuesday produced numerous size 3 persistent slab avalanches failing on facets near the base of the snowpack. The most notable results were on steep, rocky north aspects, and lower angled west aspects.
Snowpack Summary
Up to 20 cm of recent storm is rapidly settling. This snow overlies decomposing previous storm snow, old wind slabs, and sun crust on solar aspects. Cornices are large and prone to failure over the weekend due to forecast sunny skies and rising freezing levels.The upper/mid-pack is generally well settled and strong.The lower snowpack is weak with a combination of crusts and facets near the bottom of the snowpack that are widespread. The primary concern looking ahead is the potential of these deeper persistent weak layers becoming active by rapid warming of the snowpack through rising freezing levels and intense solar radiation. This is most likely to occur on steep south facing slopes.
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.
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.
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.