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Avalanche Forecast

Archived

Feb 6th, 2023–Feb 7th, 2023

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

Regions

North Rockies, Kakwa, McGregor, Pine Pass.

Continued snowfall and wind are causing dangerous avalanche conditions to persist. Human-triggered avalanches are very likely and natural avalanches continue on wind-loaded lee slopes.

Uncertainty is best managed through conservative terrain choices at this time.

Confidence

Moderate

Avalanche Summary

In the Pine Pass area, heavy snowfall caused a natural avalanche cycle that started on Thursday and continued through the weekend. Reports from Thursday indicate storm slabs were very reactive to snowmobile traffic, producing many size 1 to 1.5 storm slab avalanches that propagated widely.

On Saturday, explosives control produced several size 2 to 3 wind slab avalanches in cross-loaded alpine start zones.

On Sunday, three very large natural avalanches were observed up to size 4. Two were size 3 persistent slab avalanches on steep north-facing aspects with 750 m 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.

See more on the potential of triggering deeper weak layers in our latest Forecasters' Blog.

Snowpack Summary

Stormy weather over the past week has brought 50 to 100 cm of new snow to the region. Warm windy weather is causing storm snow to settle into reactive slabs. The storm snow sits on previously wind-affected surfaces. Below this, a melt-freeze crust is found on sun-exposed slopes and everywhere below 1600 m.

Several crust/facet/surface hoar layers exist in the upper and middle portions of the snowpack. The most concerning persistent weak layer is at the base of the snowpack from large and weak facets formed in November. This layer is widespread and most likely problematic in steep, rocky alpine and upper treeline terrain.

Weather Summary

Monday Night 

Cloudy with scattered flurries, 8-15 cm accumulation. Localized areas, particularly around Kakwa, may see higher accumulations with up to 25 cm. Alpine temperatures low of -3 C. Ridge wind southwest 60 km/h, 70-80 km/h over Kakwa. Freezing level slowly lower to 1000 m overnight. 

Tuesday 

Mix of sun and cloud with isolated flurries, 2-5 cm accumulation. Alpine temperatures drop to -6 C. Ridge wind southwest 40-60 km/h. Freezing level 1200 meters. 

Wednesday 

Mainly cloudy with sunny periods and isolated flurries, 2-5 cm accumulation. Alpine temperatures rise to -7 C. Ridge wind southwest 60 km/h easing in the afternoon. Freezing level 1000 meters. 

Thursday 

Mainly sunny with cloud increasing in the afternoon and isolated flurries, 2-10 cm accumulation. Alpine temperatures rise to -3 C. Moderate ridge wind from the southwest picks up to 50-70 km/h in the evening. Freezing level 1500 meters. 

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Keep your guard up at lower elevations. Storms slabs have been reactive at all elevations.
  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very 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.

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.