Avalanche forecast

Kootenay Boundary

Jan 31, 2018Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Dangerous snowpack conditions are widespread in the region. Numerous very large avalanches ran on deeply buried weak layers during the storm. The chances of human-triggering these deep layers remains dangerously high.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–2
    Strong southwest winds have pressed and redistributed loose snow at the surface into stiff and reactive slabs. Windward aspects aren't exempt from the problem.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–3.5
    The snowpack is complex and continues to produce very large avalanches on several weak layers buried 80 to 150 cm below the surface. A conservative approach and moderate-angled, simple terrain are good ways to manage a complex snowpack.

Confidence

Moderate -

Weather Forecast

Wednesday: A mix of sun and cloud. Light west winds. Alpine high temperatures of -8.Thursday: Cloudy with scattered flurries and 2-6 cm of new snow, increasing overnight. Light to moderate southwest winds. Alpine high temperatures of -6.Friday: Cloudy with continuing flurries and 2-5 cm of new snow. Light to moderate southwest winds. Alpine high temperatures of -4.

Avalanche Summary

Reports from Tuesday reflect increased visibility over terrain that was obscured during the storm. Evidence of a natural avalanche cycle involving each of our persistent weak layers was observed, with numerous avalanches ranging reaching Size 3.5 and several crown fractures up to 3 metres deep. These are believed to be some of the deepest crowns in the region's historical record.Reports from Monday include observations of several natural storm slab releases from Size 1.5-2 as well as numerous explosives triggered storm slabs to Size 1.5 southeast of Nelson. One Size 3 persistent slab with a fracture depth of 100 cm was observed releasing naturally in the same area. Storm slab activity was focused on north through west aspects from 1800-2100 m and the persistent slab release occurred on a southeast aspect just under 2000 m.Sunday's reports included one observation of two large persistent slabs releasing remotely on a wind loaded feature just below ridgetop in the Kootenay Pass area. Another remotely triggered Size 2.5 persistent slab was reported in the south Valhallas.Looking forward, expect storm slabs and the persistent slabs beneath them to remain reactive to human triggers.

Snowpack Summary

Recent storms have brought around 100 cm of snow to the region over the last couple of weeks. Rising temperatures delivered some of the most recent precipitation as rain below about 1300 metres on Monday. Where it fell as snow, strong southwest winds have again redistributed it into touchy new wind slabs.Aside from wind slab instabilities at the surface, the primary layer of concern from mid-January and is buried beneath all the storm snow at 80-110cm deep. It is composed of a mixture of weak surface hoar and/or a crust. Numerous recent natural avalanches to size 2.5 have been reported on this sensitive layer and human triggering large, destructive avalanches on this layer remains likely.Below this layer lies a second crust/surface hoar interface buried early-January that is now 110-130 cm deep. Several recent avalanches have stepped down to this layer.The mid-December surface hoar layer is buried 120-150 cm below the surface. This layer has continued to produce step down releases and "sudden" test results. It is most pronounced at treeline, but is also present below treeline . Two laminated crusts created by rain events in late November lay just below the mid-December interface.

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