The snowpack is creating tricky avalanche conditions, with new snow falling on buried weak layers that are showing signs of instability. Cautious route finding is advised.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Thursday
Weather Forecast
THURSDAY: Cloudy with snowfall, accumulation 10-20 cm, light to moderate southwesterly winds, alpine temperature near -12 C, freezing level below valley bottom.FRIDAY: Partly cloudy, light to moderate westerly winds, alpine temperature near -9 C, freezing level below valley bottom.SATURDAY: Partly cloudy with intermittent snowfall, moderate to strong westerly winds, alpine temperature near -8 C, freezing level near 1200 m with possible inversion conditions.
Avalanche Summary
The new 20 cm of storm has been reactive and produced small storm slabs. This has most often been observed in direct lee features as well as below treeline elevations. Around 1900 m, ongoing reports of touchy conditions have been noted, such as whumpfing and cracking.
Snowpack Summary
An unstable weak layer from mid-December (predominantly feathery surface hoar crystals and/or a sun crust) is found at treeline and below treeline elevations. Slabs can fail very easily on this layer, either naturally or with the weight of a person or machine. Forecasted new snow will continue to stress this layer and likely make it easier to trigger.The snowpack is variable across the region, but persistent slabs are generally a 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 southwest winds but more recently northerly winds, which have reverse-loaded some slopes. This means that wind slabs may be found on every aspect. 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 exist. An avalanche in motion could step down to these deeper layers, creating a large and destructive avalanche. Overall snowpack depths are variable across the region. It is 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.