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Avalanche Forecast

Archived

Jan 15th, 2021–Jan 16th, 2021

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

Regions

Sea To Sky.

Be mindful of buried weak layers. Recent persistent slab avalanches have been large, destructive and difficult to predict. This is not the time to be pushing into aggressive or committing lines. Uncertainty is best managed through conservative terrain selection. 

Confidence

High -

Weather Forecast

Friday night: Partly cloudy, light to moderate northwest wind, freezing level 700 m.

Saturday: Mix of sun and cloud, light southwest wind, freezing level 1100 m.

Sunday: Snow overnight, 5-15 cm, moderate southwest wind, freezing level 1100 m.

Monday: Mix of sun and cloud, light to moderate northerly wind, freezing level 1300 m with an above freezing layer developing.

Avalanche Summary

Explosive control work targeting cornices on Friday produced results up to size 2. On Wednesday, there were reports of a natural storm slab avalanche cycle up to size 3. There were also several that stepped down to deeper weak layers resulting in very large (size 3-4) persistent slab avalanches. Check out this MIN describing a large cornice-triggered avalanche in the Blackcomb sidecountry on Thursday.

Last Saturday, a large (size 3) avalanche was remotely triggered by skiers on Cowboy Ridge near Whistler. The avalanche occurred on a north to northwest aspect at around 1900 m. The crown ranged reached up to 200 cm and was approximately 200 m wide. Check out this MIN for photos and more information. A similar avalanche was remotely triggered by skiers on a nearby westerly slope a few days before; check out this MIN for more info and photos.

Snowpack Summary

Variable wind effect in the alpine includes scoured windward aspects, sastrugi, hard slab, wind pressed surfaces over lower density snow and isolated pockets of soft snow in sheltered areas above 2000 m. Wind slabs may remain sensitive where they overlie surface hoar in sheltered terrain or a crust on solar aspects. A widespread surface crust exists below 1900 m.

The snowpack is currently quite complex. Layers of surface hoar as well as sugary faceted grains above a hard melt-freeze crust from early December may be found down 100 to 200 cm. Last weekend, several large natural and human-triggered avalanches on this layer occurred, with the hot spots being around the Whistler backcountry.

Near the base of the snowpack, there may be faceted grains above a crust from early-November, which was identified as the failure layer in recent sporadic avalanche releases. At this depth, avalanches are large and destructive.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Cornice failure may trigger large avalanches.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • In times of uncertainty conservative terrain choices are our best defense.

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.