Storm slab problems remain the primary concern, but persistent slab problems are unfortunately alive and well. Keep factoring the possibility for large avalanches from isolated features into your terrain selection.
Weather Forecast
Tuesday: Cloudy with scattered flurries and a trace to 5 cm of new snow, increasing overnight. Moderate to strong southwest winds. Freezing level near valley bottom with alpine high temperatures around -5.Wednesday: Cloudy with continuing flurries bringing 2-15 cm of new snow, continuing overnight. Moderate to strong southwest winds. Freezing level rising to 1500 metres with alpine high temperatures of -3.Thursday: A mix of sun and cloud with lingering isolated flurries and a trace of new snow. Moderate to strong southwest winds. Freezing level to about 1200 metres with alpine high temperatures of -5.
Avalanche Summary
Reports from Monday included seven deep persistent slabs that were released with small explosives in the alpine in the Fernie area. Sizes ranged from 2.5-3, crown depths averaged about 2 metres and all results indicated the deeply buried late November crust as the failure plane. These results demonstrate the need for ongoing vigilance with regard to overhead hazards and the ongoing potential for deep, destructive avalanches to occur.Saturday's reports showed explosives control in the Fernie area producing numerous storm slabs from Size 1.5-2.5. One skier triggered Size 2 was also recorded. This activity was observed above 1700 m on all but southwest aspects. Two observations of naturally triggered persistent slabs (Size 2 and Size 3) in the Fernie were also reported.Reports from Friday included both natural and explosives triggered storm slabs from Size 1.5-3 in the Fernie area. The Size 3 was a natural, cornice-triggered slide that failed to step down to any deeper persistent weakness. All of these occurrences were focused on north to east aspects and slab depths ranged from 20-40 cm.
Snowpack Summary
About 40 cm of new snow has buried a new layer of feathery surface hoar on sheltered aspects (especially prominent from 1400-1900 m) as well as sun crust on solar aspects. Moderate to strong winds have been encouraging slab formation over this interface at higher elevations and continuously loading loose snow into deeper slabs in lee areas. The winds have also been also building up cornices along ridges. A thin rain crust may be present about 15cm below the snow surface at 1800 m and lower. This crust likely forms the new snow interface at lower elevations.Beneath the new snow, a number of buried weak layers have been very concerning over the past couple of weeks. A layer of surface hoar from early January is around 60 cm below the surface and the unstable weak layer from mid-December (predominantly surface hoar and/or a sun crust) is around 100 cm below the surface at treeline and below treeline elevations. A rain crust with sugary facets that developed late-November is near the bottom of the snowpack. All of these layers produced large, destructive avalanches in the last two weeks. Recent observations suggest that reactivity at these layers remains a real concern.
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.