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Avalanche Forecast

Archived

Feb 9th, 2023–Feb 10th, 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 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.

Regions

North Rockies, Kakwa, McGregor, Pine Pass.

Strong winds are transporting new snow into deep, cohesive slabs at treeline and alpine elevations. Avoid lee and cross-loaded terrain. Minimize exposure to avalanche terrain during times of heavy loading from wind and new snow.

Confidence

Moderate

Avalanche Summary

On Wednesday, a few natural size 3.5 avalanches were observed in wind-loaded alpine features.

On Tuesday, a skier accidental, size 1.5 storm slab avalanche was reported at 1500 m. A size 2, natural windslab avalanche was observed on a northwest aspect at 1400 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.

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

Snowpack Summary

Thursday's storm brings 20 cm of storm snow to the Pine Pass area and 10 cm elsewhere in the region. This adds to the 60 to 110 cm of recent storm snow over 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

Thursday Night 

Partly cloudy with scattered flurries, 5 cm through most of the region. Up to 15 cm accumulation in the Pine Pass area. Ridge wind from the west 40-60 km/h. Alpine temperatures low to -3 C. Freezing level 1300 m. 

Friday

Partly cloudy with isolated flurries, 5-10 cm accumulation. Alpine temperature high of -3 C. Ridge wind southwest 40 gusting 60 km/h. Freezing level 1200 m. 

Saturday

Cloudy with sunny periods and isolated flurries, 1-5 cm accumulation. Alpine temperature high of -4 C. Ridge wind west 40-60 km/h. Freezing level 1000 m. 

Sunday

Partly cloudy with isolated flurries, 5-10 cm accumulation. Alpine temperatures rise to -2 C. Ridge wind southwest 50-70 km/h. Freezing level 1500 m. 

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid all avalanche terrain during periods of strong wind.
  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
  • Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.