Avalanche forecast

Northwest Coastal

Nov 22 – 23, 2012Avalanche Canada
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Avalanche danger

Sat
Sun
Alpine
No rating
Treeline
No rating
Below
No rating
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Highlights

This bulletin is based on limited data. Local variations in conditions are likely to exist. Check out the forecaster's blog for further details on interpreting early season bulletins.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–4
    Recent northerly and easterly winds have deposited weak slabs on unusual aspects. Natural avalanche activity is expected in response to heavy wind-loading, and fresh wind slabs will likely be sensitive to human triggering.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–5
    Facet/crust combinations can propagate over large areas, are often prone to remote triggering and step down avalanches, and typical trigger points include thin rocky areas.

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

Friday: Moderate to heavy snowfall starting Thursday afternoon is expected to bring 30-50cm of new snow, with the highest amounts concentrated in immediate coastal areas, before tapering off by the evening. Freezing levels around 600-800m and mountaintop winds are expected to be extreme southwesterlies during the height of the storm, but ease throughout the day. Saturday: Continued moderate snowfall with 15-25cm possible, again heaviest for immediate coastal areas. Freezing levels remaining in the 600-800m range and strong southwesterly mountaintop winds. Sunday: A mix of sun and clouds with isolated flurries and cooling as winds shift to northwesterlies.

Avalanche Summary

Explosives control last weekend produced a couple of 30cm deep size 1.5-2 storm slab avalanches. Natural avalanche activity followed by human-triggered activity generally occurs with every intense weather period, such as what's forecast for Thursday night and Friday.

Snowpack Summary

Total snowpack depth is probably at least a metre in most treeline areas and deeper but more variable in the alpine, while below treeline areas are probably still below threshold depths for avalanches. A recent profile at 1200m in the Shames area showed a predominately "right-side-up" 120cm deep snowpack with a thin layer of facets sitting on a crust 35cm off the ground. An Extended Column Test produced easy (10 taps)  results on this persistent weak layer , but the resistant fracture didn't propagate across the entire column. Check out the Skeena/Babine discussion forum for more information from the area.

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