Avalanche forecast

South Coast

Mar 9, 2017Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Recently formed storm slabs are expected to remain reactive on Thursday, especially in wind loaded terrain.  Use extra caution on south facing slopes when the sun is out. Conservative terrain selection remains important.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–4
    Storm snow from the past week sits over a buried persistent weak layer. While this layer has gained a lot of strength recently, very large avalanches may still be possible in isolated terrain.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–2
    The storm snow from Tuesday is expected to remain reactive on Thursday, especially in wind loaded terrain.  Extra caution is also recommended on sun exposed slopes when the sun is shining.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Mainly cloudy conditions are expected on Thursday with snow flurries and sunny breaks both possible. Alpine wind is expected to be moderate from the southwest and freezing levels are forecast to reach around 800 m. A storm system is expected to reach the region Thursday evening. 30-40 cm of snow is forecast between Thursday evening and Friday afternoon. Alpine wind is forecast to be strong from the southwest and freezing levels should climb to around 1500 m on Friday afternoon. The next storm system is currently forecast to arrive on Saturday afternoon or evening.

Avalanche Summary

On Wednesday, explosives triggered two size 1 storm slabs which released down 10-25 cm.  These were described as having minimal propagation and minimal entrainment.  On Monday, a report includes whumphing and a ski cut triggering a size 2 slab which released on the crust layer.  Explosives also triggered numerous storm slabs 20-30 cm thick and one stepped down to the crust layer down 40-60 cm.  On Thursday,  recently formed storm slabs may still be reactive to human triggering, especially in wind loaded terrain. Large persistent slab avalanches have generally become unlikely but still may be possible in isolated areas. Natural sluffing is possible from steep sun exposed slopes.

Snowpack Summary

Another 25-50 cm of snow fell in the North Shore mountains on Tuesday bringing the typical storm accumulation in the past week to 100-200 cm. Recent winds have been from a variety of directions and wind slabs should be expected on all aspects. This recent snow overlies the late-February interface that is composed of a sun crust on southerly aspects and surface hoar on shaded aspects. An observation on Wednesday suggests this layer has gained a lot of strength since the weekend.  However, conservative choices are still recommended until we are sure this layer has become unreactive.  We could be in a low probability, high consequence scenario where very large avalanche are still possible in isolated areas. Below this interface, the mid and lower snowpack appear to be well settled and strong.

Regions covered