Conditions are changing. Avalanches will become more likely and more dangerous as forecast new snow amounts gradually accumulate.
Confidence
Poor - Intensity of incoming weather is uncertain
Weather Forecast
Tuesday: A Pacific frontal system arrives bringing around 5 cm new snow and strong westerly winds, which at ridge top could reach 100 km/h. Freezing levels will rise to around 1500 m in the afternoon. Wednesday: the cold front associated with the system moves through, bringing around 10 cm additional snow and bringing freezing levels down later in the day to around 1000 m. Winds should become moderate northwesterly. Thursday: Dry, with light northwesterly winds and freezing levels around 800 m.
Avalanche Summary
On Sunday, a size 2.5 avalanche was triggered remotely from 20m away. It ran on surface hoar buried 45cm below the surface on an east aspect at 2500 m. Elsewhere (and more typically), small avalanches could be triggered in the top 20 cm of snow by ski cutting. As we get incremental amounts of new snow above this interface, we inch closer to the tipping point, when more widespread and dangerous avalanches start to occur. This concept is discussed in more detail in the latest Forecaster Blog post.
Snowpack Summary
Widespread surface hoar has been buried by around 15-20cm of new snow in most of the region. The exception is terrain closer to the Bugaboos, where the interface is down 30-40cm. A melt-freeze is also associated with this weak interface on southerly aspects at all elevations. North and east aspects continue to have dry snow and some surface sloughing in steep terrain. Basal facets have not been reactive, but operators continue to monitor this layer in tests. Triggering this deep persistent weak layer is unlikely, but shallow snowpack areas or shallow weak areas adjacent to deeper wind loaded slopes are suspect locations.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.