Regions
Northwest Inland.
Attention sledders: Be particularly careful pushing into new areas that have not been heavily ridden. Lower layers are triggerable, particulary on convex features and where hard wind slabs have formed.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Friday: Dry and sunny. Winds mostly light northeasterly. Alpine temperatures around -16C. Saturday: Dry and sunny. Winds mostly light from the northeast. Alpine temperatures around -17C. Sunday: Increasing cloud. Winds increasing through the day to 40km/h southwesterly by the afternoon. Temperatures around -17C.
Avalanche Summary
A widespread natural storm cycle up to size 3 was reported that ended on Wednesday. Human triggering remains likely, especially in terrain that has not been heavily ridden.
Snowpack Summary
Up to 50 cm new storm snow now sits over a highly variable interface comprising of wind-scoured surfaces, hard wind slabs, faceted (sugary) snow, and maybe some feathery surface hoar in sheltered areas. The new appears to have bonded poorly to this interface. The winds were extreme through much of the storm, and hard wind slabs now exist behind exposed terrain features. The snowpack is still shallow throughout the region and widespread faceting of the entire snowpack is likely in most areas. A thick rain crust that formed in early November is probably near the bottom of the snowpack and is probably surrounded by sugary facets. Basal facets and depth hoar (more sugary crystals) right at the bottom of the snowpack are reportedly widespread.
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.