Avalanche forecast

Northwest Coastal

Jan 15, 2018Avalanche Canada
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Archived · expired 9 years ago

Avalanche danger

Tue
Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Strong southerly winds have amplified wind slab problems and sustained warming is testing a deeper weak layer. Play it conservative until temperatures cool off.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–2
    Strong southerly winds have been blowing new snow into wind slabs in lee terrain. Older, more stubborn windslabs from recent outflow winds may still be reactive around ridgecrests and on crossloaded features at lower elevations.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–4
    A weak layer buried about 60-80 cm may become reactive with warming temperatures. Shallower slabs may step down to it and form large, destructive avalanches. This layer may have been involved in several large avalanches in Bear Pass area on Saturday.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–2
    Warm temperatures will persist on Monday. Small loose wet avalanches may still run naturally or with a human trigger in steep terrain - especially in areas that have new snow on the surface.

Confidence

Moderate -

Weather Forecast

Monday: A mix of sun and cloud with low valley cloud due to a lingering temperature inversion. Light southeast winds. Freezing level to around 1500 metres with alpine high temperatures around +2. Cooler at lower elevations.Tuesday: Mainly cloudy with scattered flurries bringing 1-4 cm of new snow, continuing overnight. Moderate to strong south winds. Freezing level returning to about 700 metres as the temperature inversion dissipates. Alpine high temperature to -2.Wednesday: Cloudy with flurries bringing approximately 5 cm of new snow with light flurries continuing overnight. Moderate to strong east winds. Freezing level to 600 metres with alpine high temperatures of -4

Avalanche Summary

Reports from the Bear Pass area on Sunday included observations of a few naturally triggered Size 2-3 slabs releasing from northeast-facing alpine terrain. It hasn't been confirmed, but these may have run on the mid-December crust/facet interface described in the snowpack discussion. Size 1-2 wind slabs were also observed releasing naturally from crossloaded gully features below treeline. No avalanches were reported from elsewhere in the region.

Snowpack Summary

Precipitation combined with variable freezing levels delivered a mix of around 5-10 cm of new snow and freezing rain to the region on Saturday. Where the new snow exists, strong southerly winds have been blowing it into fresh wind slabs in lee terrain. Beneath the new snow, recent strong northerly outflow winds formed wind slabs on southerly and southwesterly features, so a mix of old and new wind slabs can now likely be found on all aspects in wind affected areas. Below the most recent precipitation, up to 45 cm recent snow overlies several layers of interest in the upper snowpack. These include crusts, surface hoar and facets. A hard crust with associated facets from mid-December sits deeper in the snowpack, about 60 cm down. Any of these layers could create a persistent slab problem as wind-loading and warming change the properties of the slab above.The lower snowpack is generally strong, with the exception of areas around Stewart and further north where a basal crust and facets exist.

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