Avalanche Forecast
Kootenay Boundary
A slab up to 100 cm in depth is consolidating above buried surface hoar which has recently produced large human triggered avalanches. Carefully plan and travel with intention to avoid convexities as well as steep open and/or sparsely treed slopes.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Conservative terrain selection is critical, choose only well supported, low consequence lines.
- The trees are not a safe haven, travel at treeline requires expert knowledge and diligence.
- Avoid convexities as well as steep, open and/or sparsely treed slopes at and below treeline.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Warm temperatures Tuesday likely helped the 20 to 50 cm of recent storm snow to settle and stabilize, but it may still be sensitive to human triggering, especially in steep, convex and/or unsupported features.
Travel and Terrain Advice
- Caution with wind loaded terrain especially near ridge crests and roll-overs.
- Storm slabs in motion could step down to deeply buried weak layers resulting in large avalanches.
Avalanche Summary
On Tuesday reported avalanche activity was limited to minor snowballing and pinwheeling, although a small solar induced slab released from a steep rocky feature late in the day. On Monday another avalanche failing on the mid-December interface was triggered remotely from 10 m away as a skier approached a rocky outcropping on an east/southeast facing feature around 1900 m, MIN report with photos here. A skier also triggered a small storm slab on a west facing feature around 2200 m Monday which was suspected to have failed on the late December surface hoar. On Sunday a skier was involved in an avalanche on an east facing treeline feature at Kootenay Pass, the avalanche appears to have failed on the mid-December interface. On Saturday we received two reports of large avalanches failing on the mid-December interface. The first was initiated by explosive control work, the size 2.5 avalanche ran on a 35 to 40 degree slope that was southeast through southwest facing at treeline. The second avalanche was a size 3.0 that released naturally on a 30 degree east facing slope between 1900 and 1400 m. This crown was up to 75 cm in depth.
Snowpack Summary
Last week two successive storms produced 25 to 50 cm of low density storm snow that was accompanied by moderate to strong winds out of the east, southeast, south and southwest. The new snow overlies the late December surface hoar which is 3 to 5 mm in size. We don't know much about the distribution of this weak layer yet. Warming temperatures on Tuesday began to moisten the snow surface on steep southerly aspects. Surface hoar has started to blossom on the surface recently too.
Between 60 and 100 cm below the surface you'll find the December 15th interface which consists of a melt-freeze crust on steep, solar, higher elevation slopes and well-developed surface hoar which seems most pronounced in sheltered terrain at and below treeline. The overlying slab is now deep and is gaining cohesion. This interface has hit the tipping point for human triggering as evidenced by recent avalanche activity listed above.
The lower snowpack is thought to be strong and well-settled.
Weather Forecast
Temperatures along the coast have moderated and this trend should linger through Wednesday as a southwesterly flow of mild Pacific air continues. With cold Arctic air trapped in the deep valleys of the eastern interior ranges, the warm up there will be slow. Those hoping for fresh snow will have to wait until late in the week.
WEDNESAY: Clear skies, freezing level at valley bottom, light variable wind, no snow expected.
THURSDAY: Clear skies with cloud building in the afternoon, freezing level at valley bottom, potential for a light temperature inversion in the afternoon, light southwest wind picking up through the day, no snow expected.
FRIDAY: Overcast, freezing level around 500 m, light to moderate southwest wind, trace of precipitation possible.
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Surface hoar is now buried up to 100 cm deep and has recently produced large skier triggered avalanches. This slab appears to be most sensitive at treeline, but it is present below treeline too.