Avalanche forecast

Purcells

Jan 2 – 3, 2012Avalanche Canada
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Avalanche danger

Wed
Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–4
    Winds continue to redistribute storm snow into wind slabs. I'd be suspect of any open area, even below treeline. Once moving, a wind slab could easily step down and trigger a large avalanche.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–7
    The mid-December surface hoar/ facet/ crust layer continues to be touchy. Avalanches failing on this layer are large, and destructive. They have occurred at all elevations, and may fracture wider and further than expected.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–7
    The weight of the snowpack is pushing this layer over the tipping point in some areas. Avalanches triggered from thin spots, or weak layers in the upper snowpack have the potential to step down to this layer creating a deep and destructive avalanche.

Confidence

Good - -1

Weather Forecast

An approaching pacific frontal system will bring light -moderate precipitation to the region through Tuesday. Snow amounts 5-10cms. Ridgetop winds will be 35-55km/hr from the SW. Freezing levels may rise to 1000m. Wednesday: Snow amounts near 10cms. Ridgetop winds 45-55km/hr from the SW. Freezing levels could rise to 1850m then drop to valley bottom Thursday. Thursday: Snow amounts 5-10cms. Winds light from the SW. Freezing levels drop to valley bottom.

Avalanche Summary

Over the past 48hrs a large natural cycle up to size 3.5 occurred. These avalanches ran on all aspects, and was evidence of a widespread storm cycle. Most operations proceeded with full avalanche control missions using explosives. They reported numerous large avalanches size 2-3.5 on N-NE aspects. I suspect that human triggering is likely out there creating large, destructive avalanches that may not be survivable. I would also avoid slopes with cornices overhead. They provide a substantial trigger that will very likely initiate a slide on the slope below.

Snowpack Summary

The Purcell region has seen up to 140cms since the Christmas holiday. The new snow has settled into a cohesive slab, and the average total snowpack depth is near 200cms. The ridgetop winds have consistently blown from W-SW and have redistributed the storm snow into wind slabs. Wind slabs are widespread and found in exposed alpine and treeline locations. Even open areas below treeline are suspect for wind affected snow. In sheltered areas the snow surface is starting to form surface hoar crystals (feathery), and surface facets (sugary crystals). These crystals may create a weak layer in the snowpack once buried. Below the surface down 80-140cms lurks the mid-December surface hoar/ crust, facet layer. This is a layer of concern. It continues to be sensitive to the weight of a skier or sledder. The recent load of new snow has also awoken the basil weakness near the ground on north facing slopes. This mixed bag of weaknesses has made for a very tricky avalanche situation as evidenced by the numerous accidents in the area over the last few days.

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