Avalanche forecast

Northwest Coastal

Dec 11 – 12, 2011Avalanche Canada
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Avalanche danger

Tue
Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    Expect new windslabs on east/ northeast aspects. Loading may occur lower on the slopes due to forecast high winds in some parts of the region.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2
    Storm slabs have taken shape with friday night's snowfall and will continue to develop with forecast weather.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Monday

Weather Forecast

15-20 cms of snow accompanied by moderate to strong southwest winds are expected for monday. Light to moderate snowfall with moderate southwest winds will continue for tuesday morning.On wednesday scattered cloud, minimal precipitation and light southerly winds are forecast for the region.Freezing levels are expected to remain at surface for the forecast period.

Avalanche Summary

No avalanche activity has been reported. Expect avalanche activity with current conditions and forecast weather.

Snowpack Summary

Between 10 and 20 cms of snow combined with strong to extreme westerly winds arrived on friday night.In some parts of the region, light amounts of new snow had previously buried large surface hoar that was sitting on a 5-20cm thick melt freeze crust. This crust extends into alpine elevations in the south, and around 1000m in the north. A strong temperature gradient in the top 30cm was reported to be faceting snow below the surface crust.The mid and lower snowpack are generally well settled and strong. At this point I have a few concerns: Because of the intensity of friday night/saturday morning's winds, the surface hoar may have been destroyed in some areas, but probably still exists in others. This makes it difficult to track now that the new snow is hiding it. As well, with the higher winds the distribution of the new wind slab may be less predictable and you are likely to find loading lower on the slope than usual. The new slab will also have varying propagation characteristics. For example, in areas where it is wind-affected and stiff, it will be likely to slide; however, you might not see the same reactivity at lower elevations or on the eastern fringe of the region where there may not have been as much wind. Regardless of all the speculation, there has been moderate snowfall with a ton of wind and it's sitting on a melt-freeze crust in a major portion of the region. With monday's forecast weather you can expect reactive windslab development in many parts of the region for the forecast period.

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