Storm slab problems vary by elevation band. Wind loading patterns are your guide to avoiding slabs at higher elevations. Further down, carefully manage steep, sheltered slopes that may harbour surface hoar.
Weather Forecast
Sunday: Mainly cloudy with isolated flurries and a trace of new snow, increasing overnight. Moderate to strong southwest winds. Freezing level near valley bottom with alpine high temperatures around -6.Monday: Mainly cloudy with continuing isolated flurries and a trace of new snow. Moderate to strong southwest winds. Freezing level near valley bottom with alpine high temperatures of -7.Tuesday: A mix of sun and cloud. Moderate southwest winds. Freezing level near valley bottom with alpine high temperatures of -8.
Avalanche Summary
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.Thursday's reports included a few natural storm slab releases to Size 2 from steep alpine terrain in the Fernie area, as well as loose wet releases to Size 1 with ski cutting below treeline. Explosives control targeting persistent slabs that haven't already slid was notably unsuccessful. Large explosive triggers only managed to release storm slabs to Size 2.With that said, more active persistent slab conditions are not yet a distant memory. Last week, large avalanches ran on multiple persistent weak layers, even in fairly dense trees and low angle slopes. Activity has gradually tapered off, but it would be wise to expect that the potential for human triggering remains.
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 week, and appear to be gaining strength very slowly. The early January surface hoar layer 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 were reactive and produced large, destructive avalanches in the last couple of weeks.
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.