New snow is adding stress to touchy weak layers in the snowpack.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
WEDNESDAY: Moderate westerly winds. 5-15 cm snow. Alpine temperature near -12.THURSDAY: Moderate to strong westerly winds. Light snow. Alpine temperature near -15.FRIDAY: Strong westerly winds. Light snow. Alpine temperature near -15.
Avalanche Summary
Recent observations include naturally-occurring slab avalanches at around 1900 m and ongoing reports of touchy conditions, with whumpfing and cracking observed. As snow continues to fall, avalanche activity is expected to increase.A timber sledder triggered and was caught in a small avalanche on a road cut on Sunday. It occurred a little below treeline, south of the Crowsnest. Avalanche conditions seem especially touchy in this type of terrain right now.
Snowpack Summary
A volatile weak layer from mid-December (predominantly feathery surface hoar crystals and/or a sun crust) is found at treeline and below. Slabs can fail very easily on this layer, either naturally or with the weight of a person or machine. Every extra snowflake adds stress to this layer.The snowpack is variable across the region, but persistent slabs are a generally widespread problem. Wind slab and storm slab distribution will be more variable. Hard wind slabs can be found in parts of the region due to recent extreme south-west winds. Windward alpine slopes may be scoured; and variable wind slabs are found at treeline and alpine elevations. New snow is likely to fail as storm slabs and/or loose avalanches. Deeper in the snowpack, an early season rain crust and sugary facets make up the picture. An avalanche in motion could step down to these deeper layers, creating a surprisingly large avalanche. Overall snowpack depths are variable across the region. It's generally shallower in the east.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.