Avalanche forecast

Purcells

Mar 11 – 12, 2016Avalanche Canada
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Archived · expired 11 years ago

Avalanche danger

Sun
Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Watch for new wind slab development on Saturday. Forecast snowfall amounts are uncertain, so pay close attention to how much snow falls in your area, and choose terrain accordingly.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    New snow and wind will form new wind slabs in upper elevation lee terrain. The new snow may also be hiding older, larger wind slabs which formed on Thursday.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–4
    Large cornices loom over open bowls and alpine faces. Not only are massive cornice falls a hazard in themselves, but they can also act as a heavy trigger for slab avalanches on the slope below.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–5
    A few persistent weaknesses lie buried in the top metre of the snowpack. These layers are variably reactive throughout the region, but they have the potential to surprise with nasty consequences. I'd continue riding with a conservative mind set.

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Up to 12cm of new snow is forecast to fall on Saturday with another 5cm possible in the overnight period. Generally light accumulations (~5cm) are forecast for Sunday and Monday. Ridgetop winds should be moderate from the south on Saturday, becoming light on Sunday and Monday. Freezing levels should sit at about 1800m on Saturday, and then drop closer to 1500m for the rest of the forecast period.

Avalanche Summary

On Thursday numerous naturally triggered wind slabs (mostly in the size 2 range) were observed at treeline and in the alpine. They occurred in response to new snow and wind. On Friday explosives control continued to produce storm slabs to size 2.5 on a variety of aspects throughout the region. Of note, a size 2.5 persistent slab avalanche was triggered with explosives in the Dogtooth Range. The mid-February layer was the likely culprit in the avalanche.

Snowpack Summary

Snowfall accumulations on Thursday were in the 10-20cm range. Strong southerly winds redistributed these accumulations into touchy wind slabs at treeline and in the alpine. 30-70 cm recent storm snow overlies a prominent weak layer buried on or around Feb-27. The deepest snow amounts appear to be in the west central area near Kootenay Lake. The Feb-27 weak layer comprises surface hoar and a crust. It has been widely reported but recent snowpack test results are mixed, with some tests indicating this layer is gaining strength, while others indicating it can still fail with sudden "pop" results. A deeper weak layer from mid-February is now down 50-80cm. The early January surface hoar/facet layer is typically down 70-120cm. Triggering an avalanche on either of these layers has become unlikely but either still has the isolated potential to produce very large avalanches with a heavy trigger.

Regions covered