Wind Slabs are hidden by a few cm of new snow, while deeper in the snowpack, a "Low probability / High consequence" problem lurks. If we see more snow or higher temperatures than forecast, hazard could rise to Considerable at Alpine & Treeline.
Weather Forecast
A few cm of snow forecast in flurries Tuesday and Thursday, while Wednesday is looking mainly clear and dry. Winds are forecast at Light from the West, with cool and steady temperatures, until Wednesday; when an increase to strong SW wind heralds a modest warming trend. Freezing Levels should reach the townsite by late Wednesday / Thursday.
Snowpack Summary
Upto 20cm of snow fell in the alpine on Thursday/Friday, being redistributed into Wind Slabs in the Alpine and Treeline. From Treeline down, rain formed a new crust, making for Variable ski conditions lower down. A December crust buried around a meter deep, although generally requiring large triggers, has potential to produce large avalanches.
Avalanche Summary
A small loose dry avalanche was observed in steep treeline terrain on Monday above Forum Lake. Several slab avalanches were observed on Friday near Forum and Cameron Lakes. These were small, with the exception of a Large (Size 3) slab avalanche, from a NE aspect on Forum Peak. This propagated surprisingly wide (300m) and ran onto Cameron Lake.
Confidence
Intensity of incoming weather systems is uncertain on Wednesday
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.
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.