Avalanche forecast

Northwest Inland

Dec 30 – 31, 2011Avalanche Canada
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Avalanche danger

Sun
Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–4
    Old wind slabs may still be touchy and reactive to light triggers. Watch for ne wind slabs developing with the next storm on Sunday or Sunday night.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–5
    Persistent slabs have now formed at all elevations where the mid December buried surface hoar/crust/facet layers exist. Loading by new snow and wind could be enough to wake these layers up.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–4
    The storm slab continues to grow with the incremental loading of recent snowfalls.

Confidence

Fair - Forecast snowfall amounts are uncertain on Sunday

Weather Forecast

Mostly dry conditions are forecast for Saturday, with freezing levels near valley bottoms. Moderate winds from the west are expected to become strong from the south on Sunday as the next frontal system moves in from the Pacific. Moderate to Heavy precipitation is expected for the near coastal areas, moderate for the inland areas. Freezing levels should rise on Monday combined with light to moderate precipitation and moderate southerly winds.

Avalanche Summary

No new observations from this region.

Snowpack Summary

Strong winds have been the biggest story recently. Exposed windward slopes have been scoured and wind slabs have formed in lee terrain and may be susceptible to human triggering. There is now around 55-70cms of snow sitting on a surface hoar/crust/facet combo which is the result of the early December dry spell. This crust is widespread and exists in most start zones up to 2000m. Facets can reportedly be found above or below the crust. Prior to being buried, the surface hoar was destroyed by high winds in the alpine, but still coexists with the crust at treeline and below. What is the tipping point of this weak interface? In areas where this interface has reached its threshold, natural and human triggered avalanches up to size 2.5 have occurred. If they have yet to happen, I suspect they are gaining some strength but would still react to a rider trigger, especially in steeper, unsupported terrain features. In short, the upper snowpack is variable and deserves caution. It will also see increased load with forecast wind and snow. Beneath this the midpack is well settled and strong.

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