Danger ratings are based on an expected 40cm of snowfall through Friday and Saturday, coupled with warming and strong winds. However, the weather forecast is uncertain. If less severe weather arrives, danger may be lower than forecast.
Confidence
Fair - Forecast snowfall amounts are uncertain on Saturday
Weather Forecast
Friday night: Moderate snow. Strong south-westerly winds. Alpine temperatures rising to -7C.Saturday: Moderate snow. Strong south-westerly winds. Alpine temperatures rising to -4C in the morning. Sunday: Cloud and flurries. Cooler temperatures. Moderate westerly winds. Monday: Flurries or light snow. Moderate to strong westerlies.
Avalanche Summary
Recent observations include a few cornice failures and isolated skier-triggered wind slabs in the size 1-2 range. Explosives testing released storm slabs, with little in the way of recent deep releases. Avalanche activity slowed down towards the end of the week, but is expected to increase again during the weekend.
Snowpack Summary
New storm snow is building up over wind slabs in exposed features and over loose dry snow in sheltered areas. Strong winds and warming temperatures forecast to accompany Friday night/Saturday's snowfall are likely to create a more widespread wind slab and storm slab problem. The mid-December surface hoar/facet persistent weakness, now down around 50cm on the eastern side of the range and as deep as 180cm on the western side, is still causing operators concern, especially in shallow snowpack areas. Recent snowpack tests show moderate to hard, sudden planar results on this layer. The consequences of a failure on this layer would be large. Facets and depth hoar exist at the base of the snowpack. Cornices are large and weak in some areas.
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.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.