The base of the snowpack is weak. It will remain likely for a while that humans can trigger deep persistent slabs.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
TUESDAY NIGHT: Partly cloudy, moderate west winds, freezing level below valley bottom.WEDNESDAY: Mostly cloudy, moderate to strong west winds, alpine temperature -8 C, freezing level below valley bottom.THURSDAY: Cloudy with light snowfall, strong southwest winds, alpine temperature -3 C, freezing level rising to 1500 m.FRIDAY: Cloudy with light snowfall, accumulation 5 to 10 cm, moderate to strong southwest winds, alpine temperature -5 C, freezing level 1500 m.
Avalanche Summary
No new avalanches were observed on Monday. Several loose dry avalanches and a few small (size 1) storm slab avalanches were triggered by skiers in this region on Sunday.
Snowpack Summary
Large variability in snow depths still exists in the region, ranging from practically no snow to almost 200 cm. For areas with sufficient snow, the upper snowpack consists of hard wind slabs on all aspects due to variable wind directions, a scoured and shallow snowpack on exposed southerly ridges, and generally soft snow in sheltered areas.Around 60 to 90 cm of snowfall in December has formed a slab that sits on a persistent weak layer of weak and sugary faceted snow that formed during dry and cold weather in early December. This layer is most likely to be triggered on steep features where snowpack depths are variable.The lower snowpack has a weak structure composed primarily of sugary faceted snow around a crust near the ground. Should a shallower avalanche be triggered, it is likely that it would step down and scour to the ground.
Problems
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.
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.