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Avalanche Forecast

Archived

Dec 26th, 2023–Dec 27th, 2023

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 unlikely, human triggered possible.
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

North Columbia, Blue River, Premier, Clemina, Jordan, North Monashee, North Selkirk, Robson.

Weak layers in the mid and lower snowpack have produced large natural and human-triggered avalanches in recent days.

Manage this problem with conservative terrain choices.

Confidence

Moderate

Avalanche Summary

A natural avalanche cycle occurred last Friday. Several large (size 2 to 3) storm slab, persistent slab, and deep persistent slabs were reported from the alpine and treeline.

Over the weekend, many large (size 2 to 3) natural and rider triggered (some remotely triggered) persistent and deep persistent slabs were reported in the alpine and treeline.

Moving forward, natural avalanche activity has tapered, but large human-triggered slabs remain possible.

Snowpack Summary

Recent strong winds have created heavily wind-affected surfaces in the alpine and treeline. Below treeline a new crust is on or near the surface.

The mid pack contains several layers of note; a layer of surface hoar and a crust down 20 to 40 cm, a significant crust from the early December rain event down around 50 cm and a layer of surface hoar down 50 to 90 cm.

The make up of the lower snowpack is variable throughout the region, in shallower snowpack areas, basal facets exist. This is most concerning in shallow alpine areas.

Weather Summary

Tuesday Night

Clearing. Southwest alpine wind 50 km/h dropping to 20 km/h. Treeline temperature -5 °C. Freezing level dropping to valley bottom.

Wednesday

A mix of sun and cloud. South alpine wind 20 to 40 km/h. Treeline temperature -3 °C. Freezing level rising to 500 to 1000 m.

Thursday

Cloudy with snowfall, 1 to 5 cm of accumulation. Southwest alpine wind 20 to 50 km/h. Treeline temperature -2 °C. Freezing level 500 to 1500 m.

Friday

A mix of sun and cloud with isolated flurries. South alpine wind 20 to 40 km/h. Treeline temperature -3 °C. Freezing level 1000 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Use careful route-finding and stick to moderate slope angles with low consequences.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Use ridges or ribs to avoid areas of wind loaded snow.

Problems

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.

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.

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.