Avalanche forecast

Kootenay Boundary

Jan 30, 2018Avalanche Canada
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Avalanche danger

Wed
Thu
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Seek out snow that is sheltered from wind effect to reduce the risk of triggering storm slabs, but maintain low angle, low consequence terrain selection. The same shelter has preserved deeply buried weak layers.

Avalanche problems

  • Persistent Slabs

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

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–2
    Overnight snowfall coupled with a sharp increase in winds will build touchy new storm slabs at higher elevations on Monday. Storm slab releases continue to carry a high likelihood of triggering deeper weak layers.

Confidence

Moderate -

Weather Forecast

Tuesday: Mainly cloudy with isolated flurries and a trace of new snow. Light west winds. Freezing level to 1200 metres with alpine high temperatures of -4.Wednesday: A mix of sun and cloud. Light northwest winds. Freezing level back down to around 600 metres and alpine high temperatures of -7.Thursday: Cloudy with isolated flurries and a trace of new snow. Light to moderate southwest winds. Alpine high temperatures around -5.

Avalanche Summary

Reports from Sunday included one observation of two large persistent slabs releasing remotely (from a distance) 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.Reports from Saturday showed explosives control in the Kootenay Pass area producing numerous storm slabs ranging from Size 2-2.5. Ski cutting in various areas in the region produced numerous 20-40 cm deep storm slabs generally from Size 1-1.5. A 15 cm deep mid-storm interface was noted for remote and sympathetic (by an adjacent release) triggering in the Rossland area.Explosive control near Nelson triggered numerous storm slab avalanches up to size 2 on Friday. On Wednesday, over a dozen natural size 2 storm slab avalanches were reported on all aspects and elevations, though most occurred at treeline and above. Additionally, several natural persistent slabs to size 2.5 were reported on northwest to easterly aspects above 1900m. These storm slabs and the persistent slabs beneath them are expected to remain reactive to human triggers.

Snowpack Summary

The snowpack in this region is currently being described as "Complex" and "Spooky".Another 10-20cm of new snow over Sunday night brings recent storm snow total to approximately 85-120 cm. Rising temperatures delivered much of this precipitation as rain below about 1300 metres. Where it fell as snow, moderate southerly winds have again been redistributing it into touchy new storm slabs.Aside from storm slab instabilities, the primary layer of concern from mid-January and is buried around 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 below the surface. The mid-December surface hoar layer is buried 120-150 cm below the surface. This layer still produces "sudden" test results and 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, and may co-exist with facets.

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