Avalanche forecast

South Columbia

Mar 27 – 28, 2017Avalanche Canada
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Avalanche danger

Wed
Thu
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Convective spring-like weather may bring localized higher snowfall amounts. Moderate winds continue to build reactive wind slabs at higher elevations on the leeward side of terrain features.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–2
    Recent wind from south through west directions has redistributed the new storm snow in exposed terrain at higher elevations forming reactive wind slabs.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–3
    Cornices are large and fragile. They may fail with daytime warming, sun exposure, or during stormy periods.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–4
    Sustained sun exposure or heavy triggers like a cornice fall could trigger deep, destructive avalanches on buried weak layers. This is a low probability/ high consequence scenario. If triggered these avalanches are running full path.

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Tuesday: Unsettled conditions and convective air could bring 5-10 cm of new snow with mostly cloudy skies. Ridgetop winds will be moderate from the SW and freezing levels near 1500 m. Wednesday: Snow amounts 10-20 cm. Ridgetop winds light-moderate from the South and freezing levels near 1600 m.Thursday: Cloudy with possible sunny breaks. Ridgetop winds light from the SW and freezing levels near 1500m.

Avalanche Summary

On Sunday, natural storm and wind slab avalanches up to size 2 were observed at upper elevations from northerly aspects. Explosives control and some natural cornice failures also produced slab avalanches from slopes below up to size 3. Cornices are large, fragile and are a significant hazard, especially with daytime warming or during stormy periods. The recent storm snow will likely remain reactive, especially in wind loaded terrain features at upper elevations.We are in a low probability, high consequence scenario for persistent slab avalanches failing on deep buried weak layers. Click here for more details.  Click here for new Forecaster Blog.

Snowpack Summary

20-50 cm of snow has now accumulated over the past week which overlies a rain crust below 2000 m or a sun crust on solar aspects at higher elevations. Alpine wind has recently been strong mainly from south through west directions and has loaded leeward slopes in exposed terrain at treeline and in the alpine. Large, fragile cornices are also reported along ridgelines. At lower elevations, there may be multiple crust layers in the upper snowpack which are now generally well bonded and stable. At higher elevations, the February weak layers are down 120-150 cm and woke up during last week's storm with many avalanches stepping down to them. The deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack and a few avalanches and cornice falls have also stepped down to these layers last week resulting in some very large full depth avalanches.

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