Storm slabs continue to be a concern for human triggering. This problem is more likely where a persistent weak layer of facets and/or a crust is sitting beneath the storm snow.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
Overnight: Unsettled with convective flurries resulting in 5-10 cm in some areas combined with moderate westerly winds and alpine temperatures around -15. Tuesday: A mix of sun and cloud with convective flurries and light southwest winds. Wednesday: Overcast with light snow and periods of heavy flurries combined with light southwest winds. Thursday: A mix of sun and cloud with flurries during the day, and a stronger system moving in late in the day.
Avalanche Summary
On Sunday we had reports of storm slab avalanches releasing naturally, with explosives control, and by pushing snow with a snowcat up to size 2.0. There was also a deeper release 250 cm down, suspected to have released on buried facets that resulted in a size 3.0 avalanche in the Selkirk mountains near Trout Lake. On Saturday we had reports of widespread storm slab activity.
Snowpack Summary
Just under a week of stormy weather has delivered a wide-ranging 65-120 cm of new snow to the region. Moderate to strong southerly winds accompanied the new snow, promoting touchy storm slab formation at all elevations. The new snow has buried widespread faceted surface snow, thin sun crust on steep solar aspects, as well as more isolated surface hoar to 4mm. About 90-135cm below the surface you'll find the mid-February interface which is composed of a thick rain crust up to about 1800 m, sun crusts on steep solar aspects, and spotty surface hoar on shaded aspects. This layer has seen a recent increase in more sudden snowpack test results and has been identified as a failure plane in a number of recent avalanches. Its reactivity has been especially prominent over the crust at lower elevations. Any continuing activity at this interface will likely see it emerge as a persistent weak layer.
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.