Strong winds and significant snowfall forecasted for Tuesday night and Wednesday will increase avalanche hazard. Moderate terrain with no overhead hazard is a good choice.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
TONIGHT: Snow. Accumulation 15-25 cm. Ridge wind strong, southwest. Temperature -4. Freezing level valley bottom.WEDNESDAY: Snow. Accumulation 10-15 cm. Ridge wind strong, southwest. Temperature near 0. Freezing level rising to 1500 m.THURSDAY: Mainly cloudy, flurries. Accumulation 5 cm. Ridge wind moderate, southwest. Temperature -4. Freezing level 1000 m. FRIDAY: Mix of sun and cloud. Ridge wind light, west. Temperature -3. Freezing level valley bottom.
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 200 cm 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 especially in steep rocky start zones.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 40-60 cm of storm snow now covers a layer of feathery surface hoar on sheltered aspects (especially prominent from 1400-1900 m) as well as sun crust on solar aspects that was buried mid-January. 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 mid-January interface lie a number of very concerning buried weak layers. A layer of surface hoar from early-January is around 80 cm below the surface and the unstable weak layer from mid-December (predominantly surface hoar and/or a sun crust) is around 120 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 have produced recent large, destructive avalanches and remain a 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.