Confidence
Fair - Intensity of incoming weather systems is uncertain on Saturday
Weather Forecast
Saturday: Moderate snowfall / Moderate to strong southwest winds / Freezing level at 1300mSunday: Light snowfall / Moderate to strong west winds / Freezing level at 1600mMonday: Light snowfall / Moderate southwest winds / Freezing level at 800m
Avalanche Summary
In general observations in recent days have been limited due to weather; however, several soft wind slabs to size 1 were observed running in the lee of ridge crests on Thursday. With forecast wind, snowfall and warming I would expect ongoing slab avalanche activity throughout the weekend.
Snowpack Summary
About 50cm of snow now overlies weak faceted crystals or small surface hoar that formed during the recent cold snap. On sheltered, lower elevation slopes the new snow is mostly unconsolidated; however, forecast warming and wind may enhance cohesion in snow surfaces creating a more reactive "upside-down" snowpack. Moderate to strong southwest winds have created wind slabs in exposed high elevation terrain.Professionals are still keeping their eye on the late-November interface which consists of hard sun crusts on steep south facing slopes and surface hoar in sheltered areas. This layer, buried between 40-70cm below the surface, has recently produced sudden test results and may be triggered with nasty consequences on steeper, unsupported terrain.At the base of the snowpack is a crust/facet combo that formed in October. About 60cm above the ground is a surface hoar layer which formed in early November. These layers have become generally inactive; however, residual risk of large, destructive avalanches exists, especially in areas with a thinner snowpack.
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.