Avalanche forecast

Northwest Coastal

Mar 20 – 21, 2013Avalanche Canada
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Avalanche danger

Fri
Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–4
    Watch for deep and weak wind slabs behind ridges and terrain features and in cross-loaded gullies.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–6
    Cornices are reported to be large and unstable, especially when temperatures become warm or the sun is out. A cornice fall could trigger a large slab avalanche on the slope below.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–7
    A weak layer comprising surface hoar crystals is buried around 60 cm below the surface and is reacting readily to natural and human triggers. This layer appears to have the ability to propagate over large areas of terrain.

Confidence

Fair

Weather Forecast

Thursday: Mainly cloudy and unsettled. Expect periods of convective flurries (5-10 cm) and sunny breaks. The freezing level is around 400 m and winds are moderate from the west-northwest. Friday: A ridge of high pressure brings a mix of sun and cloud. The freezing level drops to valley bottom overnight and rises to 500 m during the day. Winds are light to moderate from the northwest. Saturday: Increasing cloud with light snow developing. The freezing level rises to 600 m and winds are moderate from the southwest.

Avalanche Summary

Recent observations are limited but there are a couple new reports of rider triggered avalanches up to size 1.5 releasing on the March 9th layer down around 50 cm. A very large (size 3.5) avalanche was triggered in Cherry Bowl in the Shames backcountry on Sunday. Click here for a full report. This slide illustrates clearly the potential for deep and destructive releases on the March 9th surface hoar layer.

Snowpack Summary

30-60 cm of recent storm snow rests on a variety of old snow surfaces, including crusts, previous wind slabs and surface hoar. Warmer temperatures and recent strong winds have now set this new snow into a reactive slab, with wind slabs building in exposed areas on a variety of aspects. The surface hoar (buried March 9th) is reported to be well-developed and fairly widespread, at treeline and alpine elevations. Recent snowpack tests have produced sudden failures (pops) with moderate loading force at this interface. The mid snowpack is generally well settled and strong. Cornices are large and untrustworthy, especially when the sun is out.

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