Avalanche forecast

Kootenay Boundary

Feb 26 – 27, 2012Avalanche Canada
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Avalanche danger

Tue
Wed
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–5
    Stiff windslabs from last week are buried beneath new soft windslabs in the alpine and at treeline. Northeast winds on Sunday night may build new windslabs on S-SW aspects.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–7
    The Feb 08 surface hoar/facet/crust combination is now buried by up to a metre of new snow. As the snow above consolidates into a cohesive slab, avalanches triggered on this layer will become very large and destructive.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–3
    The 50 cm of storm snow that has fallen in the past two days has settled into a soft slab. The storm slab is sitting on top of the old windslabs and the Feb 08 persistent weak layer. Dry snow on north aspects is available for transport.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Monday

Weather Forecast

The ridge of high pressure should have moved into the region by Monday morning causing mostly clear skies and cooler overnight temperatures. Strong solar radiation may bring warm temperatures at or above freezing on southerly aspects. Some valley cloud is forecast for the Columbia and Kootenay valleys. Temperatures are expected to drop down to near -14.0 in the alpine Monday night during clear skies and light northerly winds. High pressure should continue for Tuesday, and warm temperatures are expected on sunny alpine slopes. Shaded aspects are expected to remain cool and dry. Some cloud should move into the region by Tuesday evening. Forecast snowfall amounts are unsure for Wednesday at this time.

Avalanche Summary

Explosive control in the region on Saturday produced avalanches up size 2.5 in the 30 cm of storm snow. Some skier remote triggered avalanches failing on the persistent weak layer continue to be reported from the region. The 50 cm of storm snow as of Sunday 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 100 cm have the potential to be very destructive.

Snowpack Summary

Another 20 cm of dry light new snow on Saturday night and Sunday morning has combined with 30 cm from Saturday morning to add 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 100 cm and resulting avalanches could easily be large enough to bury, injure or kill a person. 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.

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