Conditions will be tricky to manage this weekend, as a touchy surface hoar layer is buried only on some slopes and not others. Make constant snowpack assessments as you travel and take a cautious approach to terrain selection.
Confidence
Fair - Due to variable snowpack conditions
Weather Forecast
Saturday: Light W wind. Alpine temperature near -15. Trace of snow.Sunday: Light NW wind. Alpine temperature near -14. No snow.Monday: Light W wind. Alpine temperature near -10. Light snow.
Avalanche Summary
A natural cycle of size 1-2.5 storm slabs occurred over the last few days. Skiers also triggered avalanches up to size 2, failing on buried surface hoar or facets. The touchy nature of the buried surface hoar has been revealed by skier-remote triggered avalanches, and a skier-triggered size 1 which ran across a flat bench and triggered a size 2 on another slope. These events were in the 1350-1450m elevation band on N/NE aspects in the south of the region.
Snowpack Summary
New snow has developed into slabs, with a weak bond to old snow surfaces including surface hoar (found especially below about 1600 m in sheltered areas) and facets. Variable amounts of storm snow (25-90 cm) fell across the region, leaving the buried surface hoar at a prime depth for human-triggering. Recent winds have left wind slabs in the lee of terrain breaks such as ridges and ribs at alpine and treeline elevations. In areas sheltered from the wind, fast-moving sluff could throw you off your feet or carry you into a terrain trap. A strong mid-pack overlies a weak facet/crust layer near the base of the snowpack.
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.