Avalanche forecast

Kootenay Boundary

Dec 8 – 9, 2014Avalanche Canada
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Avalanche danger

Wed
Thu
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

A strong Southwest flow is expected to bring strong winds and rapidly rising freezing levels. Expect avalanche danger to increase as the storm develops.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–5
    Warming combined with increased loading from new snow or rain may increase the deeply buried slabs sensitivity to human triggers. Watch for thin spots around boulders or small trees that may be easy to trigger and then propagate to deeper areas.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    Forecast wind combined with new snow or rain may result in a touchy storm slab. Watch for conditions changing with elevation.

Confidence

Fair - Intensity of incoming weather systems is uncertain

Weather Forecast

A strong southwest flow will bring moderate to locally heavy precipitation from Tuesday to Thursday with some weather models calling for up to 50mm of rain or snow (depending on elevation) over the forecast period. Freezing levels are expected to peak at about 2300m on Tuesday and Wednesday, and then drop to about 1900m on Thursday. Strong southwest winds are forecast for the entire period.

Avalanche Summary

The new storm slab is the immediate concern as it has produced a few avalanches to size 2 in northeast-facing alpine terrain in the southwest corner of the region. Avoid freshly wind loaded features at higher elevations. The more complex problem is the lingering persistent weak layer of buried hard rain crusts with weak facets or surface hoar at the interface. Rising freezing levels during the forecast storm combined with the chance of heavy loading from rain or wet snow may be enough to weaken the bond at the crust.

Snowpack Summary

The developing storm slab is variable across the region. In the Monashee range near Big and Little White we have reports of a 25 cm storm slab that has been transported by the wind at higher elevations and it is sitting on a weak layer of facets or surface hoar. This storm slab is giving easy results from light forces in snow profile tests. The new storm slab is reported to be thinner near Nelson where it is sitting on a thin re-frozen rain crust. In the Kootenay Pass area the new storm slab is about 20 cm and may be sitting on surface hoar, and then another layer of about 20 cm (40 cm total) above the hard November 29th crust. The November 20th crust may be anywhere from about 40 cms above the ground in deeper snowpack areas to on the ground or non-existent in shallower snowpack areas. The November 20th crust continues to give moderate planar results in snow profile tests in some areas; that means the right combination of load and terrain features may result in an avalanche down to this buried layer.

Regions covered