Rider triggered avalanches on persistent weak layers remains possible at lower elevations. Terrain like cutblocks, steep forest openings and gullies are still suspect. At upper elevations wind slabs are the primary avalanche concern.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
TUESDAY NIGHT: Cloudy, trace accumulations, light northwest wind, alpine temperature -13 C.WEDNESDAY: Cloudy with light snowfall, accumulation 1-5 cm, light to moderate northeast wind, alpine temperature -11 C.THURSDAY: Cloudy with sunny breaks, light west winds, alpine temperature -10 C.FRIDAY: Cloudy, light snow, light west winds, alpine temperature -10.
Avalanche Summary
There was evidence of many small to large (size 1 to 2) natural wind slab avalanches in the region over the last three days. More recently ski cutting has produced small avalanches over convex features at various elevations. Sled cuts were still producing slab avalanches at lower elevations on cut banks and cutblock type terrain on the last South Rockies Field Team trip to this region. There was also evidence of 40 cm slabs scrubbing to ground in very shallow snowpack areas.
Snowpack Summary
Around 20 to 30 cm of snow fell within the past three days, with the highest amounts in the south of the region. The snow likely has slab properties where it has been wind affected at higher elevations and open areas. It could be more loose in sheltered areas.The mid-January layer weak layer is buried around 50 to 80 cm. The weak layer is surface hoar on shaded and sheltered slopes and is most prominent between 1600 m and 1900 m but has been found up to 2200 m. In some areas the weak layer is made up of sugary faceted crystals over old wind slab or a crust. Snowpack test results suggest that this layer may still be triggered by humans.The middle of the snowpack is generally consolidated. The bottom half of the snowpack is unconsolidated and composed of weak and sugary faceted grains. There is potential for shallower avalanches to step down to these deeper weak layers.
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.