The shallow weak snowpack continues to be a concern for triggering large avalanches.
Confidence
Moderate - Wind speed and direction is uncertain
Weather Forecast
FRIDAY: Cloudy with sunny periods, moderate west winds easing throughout the day, freezing level around 1200 m.SATURDAY: Mix of sun and cloud, light southwest winds, freezing level around 1000 m.SUNDAY: Cloudy with isolated flurries, light south winds, freezing level around 800 m.
Avalanche Summary
On Thursday, avalanche reports were limited to a size 1 skier triggered wind slab on a steep convex below treeline feature. We continue to be concerned about triggering the weak faceted layers in the snowpack, and our uncertainty revolves around what type of loading or weak spots are required for human triggering.
Snowpack Summary
Recent flurries and winds have formed thin wind slabs on lee features in exposed terrain at all elevations. The lower snowpack is quite variable throughout the region and the structure depends on snow depth. In deeper snowpack areas, the snowpack appears to be well settled and right side up with isolated concerns about the mid-December facet layer buried 50 to 100 cm deep. In shallow snowpack areas and lower elevations, the snowpack is heavily faceted. If a persistent slab is triggered from thinner snowpack areas it may release on basal facets resulting in a full depth avalanche.
Problems
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.
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.