Confidence
Fair - Intensity of incoming weather systems is uncertain on Thursday
Weather Forecast
Wednesday: Dry in the morning with flurries in the afternoon. Treeline temperatures around -5C. Winds NW 30-40 km/h at ridgetop.Thursday: 10-15 cm new snow expected. Freezing levels rising briefly to around 1500 m in the afternoon. Winds W 60-80 km/h at ridgetop.Friday: 2-5 cm new snow expected. Temperatures around -7C. Winds around 30 km/h from the NW.
Avalanche Summary
Two small (size 1) avalanches were reported on Monday, one on a E aspect and one on a NW aspect, triggered from ski-cutting the upper storm snow.
Snowpack Summary
Snowpack depths in this region average around 140-190 cm. 20 cm of recent storm snow has been reported to be poorly bonding to the older snow below. A weak layer consisting of surface hoar crystals, stellar crystals and/or a crust lies around 30-50 cm below the surface. At around 60-90 cm, another weak layer exists. This one was buried early December and comprises surface hoar, facetted snow, and/or a crust. It has shown variable reactivity in recent snowpack tests, but many professional operators are considering it carefully.There are two deeper layers of note. The late-November persistent weak layer consists of a sun crust on steep south facing slopes and surface hoar in sheltered areas and is now buried 70-110cm below the surface. The October deep persistent weak layer consists of a layer of facets sitting on a crust at the base of the snowpack. This layer is predominantly found on northerly aspects at treeline and in the alpine. The depth of both these layers makes directly triggering an avalanche on them unlikely (maybe a heavy load on a thin spot in steep terrain). Their presence could, however, increase the size of a potential avalanche through step-down.
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.
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.