There will continue to be a slow accumulation of low density new snow in the coming days.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Friday
Weather Forecast
FRIDAY: Flurries, accumulation 5cm during the day and another 5-10cm overnight / Light south southwest wind / Alpine temperature -11 SATURDAY: Cloudy with isolated flurries / Light to moderate west wind / Alpine temperature -12 SUNDAY: Mix of sun and cloud / Light northwest wind / Alpine temperature -10
Avalanche Summary
Recent reports continue to show both natural and human triggered loose dry avalanches in steep terrain to size 1 in areas that have not been affected by wind. Additionally isolated wind slab avalanches have been reported in the alpine to size 1. Expect continued potential for triggering loose dry avalanches in steep terrain and consider the potential to trigger persistent slabs where last week's storm snow has settled into a cohesive slab.
Snowpack Summary
Low density new snow is beginning to accumulate and bury a recently formed layer of weak feathery surface hoar and/or sugary facets. A layer buried mid-December that consists of surface hoar, sun crust and/or sugary facets is down approximately 30-50cm. The bond at this old snow interface is of critical importance where the overlying storm snow has consolidated into a slab. The most concerning areas are those that saw pronounced surface hoar development before the storm, such as sheltered areas at and below treeline and any area where the surface hoar may have formed on top of a sun crust. Recent snowpack tests show wide ranging reactivity on this layer but suggest that it may be most reactive on northerly aspects. A rain crust that formed in late November is now buried 60-100cm deep. Recent reports show this layer to be unreactive at this time.
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.
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.