Wind slabs may be building at higher elevations where there is still dry snow. Continued warm conditions means loose wet avalanches remain a concern during the heat of the afternoon.
Weather Forecast
A mix of sun and cloud is expected for Friday with freezing levels reaching around 2500m and moderate-strong SW winds in the alpine. The north end of the region could see light scattered precipitation on Friday. On Saturday, light precipitation is expected and models are currently showing 2-6mm. Freezing levels are forecast to fall to below 1500m by Saturday afternoon. Alpine winds should remain moderate-strong from the SW. A mix of sun and cloud is expected for Sunday with freezing levels around 2000m.
Avalanche Summary
A widespread natural avalanche cycle to size 2.5 occurred on Monday during the storm. These were primarily storm slab avalanches but several stepped down to deeper persistent weak layers or to the ground in steep unskiable terrain. At lower elevations, loose wet avalanches up to size 2.5 were reported as well as isolated wet slabs. On Friday, wind loaded areas are the biggest concern. New wind slabs will be touchy and may overload older wind slabs in leeward terrain features. Loose wet avalanches are a concern on sun-exposed slopes during the heat of the afternoon or areas that receive rain.
Snowpack Summary
The recent storm snow is settling into a cohesive slab which is typically 30-40cm thick. This snow is now moist or wet on all aspects and elevations except high elevation north facing terrain. Wind affected snow is expected in the high alpine and ongoing winds may be adding additional load to slabs in leeward terrain features. Up to at least treeline elevation, the snowpack below the new storm snow is moist or wet from the warming and heavy rain last week. A weak rain crust sits between the storm snow and the lower snowpack. The thick mid-February crust has broken down and is no longer supportive. There are a couple older persistent weak layers in the midpack that are probably breaking down but will remain an isolated concern while the snowpack remains warm.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
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.
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.