Avalanche forecast

Kootenay Boundary

Jan 20 – 21, 2015Avalanche Canada
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Avalanche danger

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

The weekend storm snow sits on a weak layer and touchy conditions may persist for several more days. The deep mid-Dec layer remains a concern and isolated avalanches continue to step down to this layer.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–4
    Strong SW winds during the storm created wind slabs in the alpine and isolated areas at treeline.  These slabs are up to 50cm thick and may overlie a layer of surface hoar.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3
    Around 30cm of snow sits on the widespread mid-Jan surface hoar/crust layer. The distribution of the slab reactivity is still uncertain so use an investigative approach.  Watch for signs of a widespread instability in your local area.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    3–6
    The mid-Dec weak layer should remain on your radar as it still has the potential to produce large avalanches. Smaller avalanches or cornice falls have the potential to trigger this deeper weakness.

Confidence

Fair

Weather Forecast

A ridge of high pressure should keep the region dry until Friday. On Wednesday, mostly sunny conditions expected with freezing levels around 800m and light alpine wind. On Thursday, mostly sunny conditions expected again with freezing levels around 1000m and alpine wind increasing to moderate from the SW-W. Late-Thursday, a temperature inversion may form and an above-freezing layer of air is possible in the alpine. This warm air in the alpine is forecast to persist for Friday but there is some uncertainty whether the valleys will stay cold or not. On Friday, mostly cloudy conditions are expected and alpine winds are forecast to be moderate-to-strong from the SW-W. A weak frontal system is expected for Friday night.

Avalanche Summary

On Monday, a natural size 1.5 storm slab was reported.  This released down 25-40cm on the mid-Jan surface hoar.  Also reported were a few ski cuts and explosive triggered avalanches. These were typically size 1.5-2 and released on the mid-Jan layer. These occurred on north through east aspects between 1900 and 2100m. On Sunday, a skier remotely triggered a size 2 avalanche on the mid-Dec weak layer down around 50cm on an east aspect at treeline. A ski cut produce a size 1 avalanche on the mid-Jan weak layer down around 25cm. Explosives triggered several storm slabs up to size 2 on all aspects. Natural avalanche activity is generally not expected on Wednesday but remains possible in isolated areas such as steep sun exposed slopes.. Human-triggering is likely in wind loaded areas and steep terrain features, especially where surface hoar underlies the recent storm snow.

Snowpack Summary

Around 30cm of recent storm snow sits on the mid-Jan surface hoar layer. In many places the surface hoar sits above a thin crust that can be found up to about 1900m on north aspects and all the way to ridgeline on south aspects. A deeper crust/surface hoar combo buried in mid-December continues to be a concern. This layer can typically be found down 70-100cm. The reactivity of this deep persistent weak layer appears to have become isolated but still has the potential for large, destructive avalanches in some areas. The layer has been the most reactive at and just below treeline.

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