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Avalanche Forecast

Archived

Jan 21st, 2023–Jan 22nd, 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 possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Kootenay Boundary, Bonnington, Kootenay Pass, Norns, Rossland, South Okanagan, Ymir, Moyie, St. Mary.

Large to very large avalanches continue to be produced from our complex snowpack.

Don't let today's sun lull you into compromising terrain.

Seek out low-angle terrain that has a deep snowpack.

Confidence

Moderate

Avalanche Summary

Avalanche control work done on Friday produced very large (up to size 3.5) avalanches. These were from our persistent problem and deep persistent problem. Under the right circumstances, riders can trigger these layers. Heavier loads like those created by smaller avalanches will trigger these deeper layers as well.

Snowpack Summary

In exposed areas, northerly winds have been redistributing 10 to 15 cm of new snow, likely creating small wind slabs in a reverse loading pattern. In many areas the new snow accumulated on a thin rime or freezing rain crust that formed in the region on Jan 18, a new layer of concern for us to watch over the near term.

Including the new snow, about 30 to 40 cm has been settling and bonding to an older mix of wind-affected and sheltered lower-density storm snow above about 1700 m and to a rain crust from mid-January at lower elevations.

A more problematic layer of weak surface hoar from early January now sits preserved 50 to 70 cm deep, especially prevalent in sheltered terrain at the treeline. This layer has been identified as the failure plane in many recent avalanches in the region and remains reactive in snowpack tests.

Another problematic layer composed of a facet/crust combination is down 60 to 90 cm (and 2 to 10 cm thick at treeline elevation). Below this, the mid-pack is settled and consolidated.

A concerning and weak layer of facets and crust 20 to 50 cm thick make up the basal snowpack.

Check out an awesome state of the snowpack video update HERE.

Weather Summary

Saturday Night

Cloudy, snow tapering off during the night with 3 cm accumulation, 35 km/h southwest wind, temperatures -8 C at 1500 m.

Sunday

Sunny, no accumulation, 40 km/h northwest winds, temperatures around -8 C at 1500 m.

Monday

A mix of sun and cloud with clouds easing towards the end of the day, no accumulation, 30 km/h west winds with gusts to 50, temperatures around -5 C at treeline.

Tuesday

Sunny with cloudy periods, no accumulation, 15 km/h west wind gusting to 50, temperatures -5 C at 1500 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.

Problems

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.

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.