The combination of recent heavy snowfall and buried weak layers has created very dangerous avalanche conditions. Several large, destructive avalanches have occurred in the past week. Travel in avalanche terrain is not recommend.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
TONIGHT: Cloudy, light flurries. Accumulation 3-8 cm. Ridge wind light, southwest. Temperature -10. Freezing level valley bottom.SATURDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind light to moderate southwest. Temperature -4. Freezing level valley bottom.SUNDAY: Cloudy, light flurries. Accumulation trace. Ridge wind light southwest. Temperature -4. Freezing level valley bottom. MONDAY: Cloudy, flurries. Accumulation 5-15 cm. Ridge wind strong, southwest. Temperature +1. Freezing level rising to 1900 m.
Avalanche Summary
Several large and very large avalanches have occurred in the past five days highlighting that very dangerous avalanche conditions exist within the region.Explosive control work on Friday produced numerous large and one very large, Size 4, deep slab avalanche that failed on the mid-December layer, 250 cm deep, on a northeast slope at 2100 m. This avalanche destroyed several large trees and ran well below treeline to the full extent of the runout zone.On Wednesday and Thursday, numerous natural, skier and explosive triggered storm slab avalanches up to Size 3 were reported with crowns from 20-80 cm deep, and propagations from 20 up to 150 m wide.On Tuesday a Size 2 was triggered from 50 m away by a snow machine on a northeast aspect at 2050 m. The crown was 120 cm deep and is suspected to have failed on the mid-December weak layer.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.
Snowpack Summary
About 60-80 cm of settled storm snow now covers a layer of surface hoar on sheltered aspects (especially prominent from 1400-1900 m) and sun crust on solar aspects, that was buried mid-January. Beneath the mid-January interface lie a number of very concerning buried weak layers. A layer of surface hoar from early-January is buried 90-110 cm below the surface. A weak layer buried mid-December (predominantly surface hoar and/or a sun crust) is around 120-160 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 and is now buried 200-250 cm below the surface. All of these layers remain active and have produced recent large, destructive avalanches.
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.