Avalanche forecast

Kootenay Boundary

Mar 24 – 25, 2013Avalanche Canada
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Avalanche danger

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

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–5
    With solar radiation and warm daytime temperatures, cornices will become unstable. There is a chance the weight of a cornice dropping onto the slope below could trigger an avalanche on the March 15th crust.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–5
    Snow has been reacting readily to human triggers on a buried crust around 40 cm below the surface. It may be more reactive in areas that have been slightly affected by the wind.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–3
    Solar aspects are likely to see loose snow avalanches on solar aspects when the sun comes out and temperatures start to warm. There is a danger that surface avalanches may step down to pull out slabs on the buried crust.

Confidence

Good

Weather Forecast

A fairly benign, spring-like weather pattern has set up through the forecast period.  Monday: A surface ridge will remain as a weak warm front moves through the western parts of the region. Skies will be sunny with high scattered cloud and no significant precipitation. Ridgetop winds will be light from the West and high diurnal temperature swings will persist. Treeline temperatures near -3.0 and afternoon freezing levels may rise to 1600 m. Tuesday/Wednesday: Mostly sunny skies with a bit more cloud cover on Wednesday. Freezing levels will hover around 1700 m in the afternoon. Treeline temperatures steady -3.0 and ridgetop winds will stay light from the West.

Avalanche Summary

Late on Saturday an avalanche fatality occurred in the Hell Roaring riding area located in the eastern ranges of the region. We have very limited information as the investigation is ongoing. At this point it sounds like a size 3 machine triggered slab avalanche. Additionally a skier triggered slab avalanche size 1.5 occurred in the Whitewater area (outside the ski area boundary). This avalanche was triggered from the leeward side of a cross-loaded feature and ran on a buried crust around 1980 m on a North aspect. On Thursday, several size 1.5-2 avalanches were either deliberately ski-cut or accidentally triggered on a range of aspects at elevations from 1800 - 2100 m. All failures were on a crust, typically buried 20-40 cm down.

Snowpack Summary

Between 20 and 80 cm of recent storm snow is settling into a cohesive slab overlying a thick crust that exists up to ridge top. The crust appears to have gained some strength in most places, but may still host a poor bond above 1800 m.  In some places, you may find an additional thinner crust within the top 60 cm snow. This has been reactive to skier triggers. A buried surface hoar layer sits approximately 80 cm below the surface and continues to fail in a sudden planar fashion when tested. In some places it may not be a concern due to the thick supportive crust that lies above it. However, it may be more susceptible to a trigger from a variable, thin snowpack area or a large trigger like a cornice fall or a snowmobiler.Large fragile cornices loom over many slopes. These may become weak and fail under the influence of the sunshine. Cornice fall can act as a large trigger on slopes below, and may trigger a deeper instability if it exists.

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