Avalanche forecast

Kootenay Boundary

Feb 25 – 26, 2012Avalanche Canada
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Avalanche danger

Mon
Tue
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–6
    New snow and moderate southwest winds are creating new windslabs in the alpine and at treeline. Stiff old windslabs will be buried and may be difficult to identify because of the new snow. Soft new slabs may trigger deeper weak layers.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    3–8
    A persistent weak layer (PWL) of surface hoar, facets and crusts continues to be buried deeper by new snow and windslabs. Avalanches that step down or are triggered on this layer will be large and destructive.

Confidence

Fair - Forecast snowfall amounts are uncertain on Sunday

Weather Forecast

Another 5-8 cm of snow is expected from flurries during the evening and overnight into Sunday. The freezing level should drop back down to valley bottoms. Sunday is forecast to be a mixed bag of convective flurries and some sunny periods, with the freezing level rising up to about 700 metres. High pressure should have moved well into the region by Monday, bringing mostly clear skies and light north or northeast winds and cooler temperatures. The region should continue to be under the influence of high pressure on Tuesday. Expect clear skies and cold overnight temperatures.

Avalanche Summary

The recent cycle of widespread natural avalanches running on the Feb 08 surface hoar is probably over. Explosive control and human triggering continue to produce avalanches on this persistent weak layer (PWL). The 30cm of light new snow may be enough to cause some more natural activity on the PWL in areas that did not recently slide and have enough wind to develop a heavy windslab load. The new snow and wind may develop a soft surface slab that does not cause the PWL to fail , but may be large enough on their own to injure or bury a person. Avalanches that release on the PWL that is buried down about 70 cm have the potential to be very destructive.

Snowpack Summary

About 30 cm of light new snow has added to the load above the highly reactive persistent weak layer (PWL), comprising large surface hoar in sheltered areas and a sun crust on solar aspects. This PWL is now buried by about 40-80 cm and resulting avalanches could easily be large enough to bury, injure or kill a person. Snowpack tests on the PWL in the Kootenay Pass area were showing ECTP Moderate down 70 cm. Professionals throughout the region are treating this layer with extreme caution, since it is showing signs of remote triggering and the ability to propagate in low angled terrain. Strong winds earlier in the week have created stiff windslabs that have been cracking and propagating long fractures. The new snow may make it difficult to identify these windslabs especially in openings at treeline and below. In the alpine there may be enough wind to create new windslabs that are softer and probably will not bond well to the old surface. In shallow snowpack areas concerns remain for the mid-December persistent weakness down around 80-100cm and for basal facets. Treeline snowpack depths are approximately 230 cm.

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