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Avalanche Forecast

Archived

Feb 7th, 2023–Feb 8th, 2023

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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
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 have created dangerous avalanche conditions, especially around wind-loaded slopes. Sheltered terrain will likely offer the best and safest riding.

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

Confidence

Moderate

Avalanche Summary

On Monday, a natural wind slab avalanche, size 2 was observed on a northerly aspect at 1900 m.

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 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.

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

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

Snowpack Summary

An additional 10 cm of snowfall throughout the region, 23 cm in Kakwa, brings storm snow totals to 60-110 cm. 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

Tuesday Night

Mainly cloudy with isolated flurries, 5-10 cm accumulation. Alpine temperatures drop to -10 C. Ridge wind southwest 40-60 km/h. Freezing levels fall to valley bottom. 

Wednesday 

Mainly cloudy with isolated flurries, 2-5 cm accumulation. Alpine temperatures -10 C. Light west ridge wind westerly increase to 40-50 km/h in the evening. Freezing level 800 meters. 

Thursday 

Partly cloudy with isolated flurries, 5-10 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. 

Friday

Partly cloudy with isolated flurries, 5 cm accumulation. Alpine temperatures rise to -2 C. Ridge wind southwest 40-60 km/h. Freezing level 1200 meters. 

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Seek out sheltered terrain where new snow hasn't been wind-affected.
  • 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.