Avalanche Forecast
North Columbia
Very dangerous avalanche conditions have developed in the Columbias. Travel in avalanche terrain is not recommended.
A Special Public Avalanche Warning is in effect in this region.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- The new snow sits on a persistent weak layer and will require more time than usual to stabilize.
- If triggered, the storm slabs may step down to deeper layers and result in large avalanches.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Light triggers have released large avalanches on this layer, which is buried around 50 to 100 cm deep in the snowpack. Storm slabs are regularly stepping down to this layer. When triggered, it is producing large, destructive avalanches that run far.
Travel and Terrain Advice
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Numerous large avalanches have run on this layer in well supported, treed terrain.
Avalanche Summary
Reports from Wednesday show a continuation of recent heightened avalanche activity involving both storm slabs above the January 5 surface hoar layer as well as the deeper December 15 surface hoar. Avalanche activity on these interfaces continues to be extensive, with natural and remote (from a distance) triggers forming a large percentage of observations. Sizes have ranged from Size 1-3, slab depths have generally ranged from 40-80 cm, and activity was observed on all aspects and elevation ranges. Reports from the previous two days showed similar activity.
Some of the notable themes that are emerging from recent activity include accidental and remote triggering, 'step down' release types, releases on surprisingly low angle, supported terrain, and wide fracture propagations.
Looking forward, expect a continuation of heightened human triggering potential that may increase toward the weekend with forecast warming.
Snowpack Summary
Recent storms have brought 40-70 cm of new snow to the region. This new snow sits on surface hoar on sheltered slopes as well as sun crust on steep solar aspects. Numerous storm slab avalanches resulted as the new snow formed a slab before bonding to the surface. Moderate to strong southwest winds accompanied the snowfall at higher elevations, creating wind slabs in lee features.
As the new snow consolidates, it forms a dangerous slab above several persistent weak layers that exist in the snowpack. The first of these is the surface hoar that exists at the new snow interface. Recent snowpack tests and avalanche activity show a high degree of reactivity at this layer. Below it, the December 15 surface hoar is now buried 50 to 100 cm deep. This layer has been the failure plane in many recent destructive slab avalanches, with many of these 'stepping down' to this layer from shallower releases. Its reactivity has been most apparent at treeline and below.
Deeper in the snowpack at depths of about 90 to 150 cm, a rain crust from November is considered dormant but could be triggered in thin spots around variable snowpack areas in the alpine.
Weather Forecast
Friday: Mainly cloudy. Isolated flurries and 2-5 cm of new snow overnight. Light southwest winds. Alpine high temperatures to -6.
Saturday: Mainly cloudy. Light to moderate west winds. Freezing level rising to 1300 metres with alpine high temperatures to -3.
Sunday: A mix of sun and cloud. Light southwest winds. Freezing level rising to 1800 metres with alpine high temperatures to +2. Cooler at lower elevations due to a temperature inversion.
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Many avalanches have been human-triggered in the recent 40 to 70 cm of storm snow. The snow is sitting on weak surfaces and it is not bonding well to them. Storm slabs are likely to be especially reactive where they have been affected by the wind.