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Avalanche Forecast

Archived

Feb 12th, 2023–Feb 13th, 2023

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

North Rockies, Kakwa, McGregor, Pine Pass.

Steady snowfall through Monday will continue to form fresh and reactive storm slabs primed for human triggering on steep slopes across the region. Triggering a storm slab or wind slab on the surface is probably the most effective way to cause a large and destructive step down avalanche.

Confidence

Moderate

Avalanche Summary

Recent observations have shown a trend away from very large persistent slab and deep persistent slab avalanches and toward surface instabilities such as wind slabs. We expect this trend to continue, however the basal snowpack remains questionable and should still figure into terrain selection around steep features with shallow or variable snowpack areas where these layers may be more easily triggered by a person or machine as well as large wind slab or cornice releases.

As recently as last week, very large natural avalanches were observed failing on deep snowpack layers. Two were size 3 persistent slab avalanches on steep north-facing aspects with 750 m wide crowns. A size 3.5-4 deep persistent slab avalanche was also observed. It is suspected this avalanche failed in depth hoar at the base of the snowpack.

Snowpack Summary

Another 15-30 cm of new snow should accumulate in the region by end of day Sunday, adding to roughly 80 to 130 cm of recent storm snow from steady stormy weather over the past week that has accumulated most recently under the influence of strong to extreme southwest wind.

Aside from shorter term storm slab and especially wind slab problems associated with successive snowfall and wind events, the recent storm snow is reportedly forming a good bond with previously wind-affected surfaces as well as the late January melt-freeze crust found on sun-exposed slopes and on all aspects below about 1600 m.

Several strengthening crust/facet/surface hoar layers can still be found in the upper and middle portions of the snowpack. The most concerning persistent weak layer, however, is at the base of the snowpack and composed of large and weak facets formed in November. This layer is strengthening slowly as well, remaining most likely to be triggered in thin, rocky alpine and upper treeline terrain.

Weather Summary

Sunday night

Cloudy with continuing snowfall bringing 10-20 cm of new snow. Strong to extreme southwest winds easing in the morning.

Monday

Cloudy with scattered flurries bringing another 5-10 cm of new snow. Light to moderate southwest winds easing and shifting west. Treeline high temperatures around -7.

Tuesday

A mix of sun and cloud. Light northwest winds shfting southwest. Treeline high temperatures around -10

Wednesday

Increasing cloud with isolated flurries. Moderate southwest winds. Treeline high temperatures around -8.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Use careful route-finding and stick to moderate slope angles with low consequences.
  • Storm slabs in motion may step down to deeper layers resulting in large 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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.