Avalanche forecast

Purcells

Jan 24 – 25, 2015Avalanche Canada
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Archived · expired 12 years ago

Avalanche danger

Mon
Tue
Alpine
4 · High
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

High freezing levels with rain and strong winds mean that the snow pack may take time to stabilize. Conservative decision making is still recommended.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    2–5
    A weak layer of surface hoar crystals is buried between 50 and 80 cm below the surface, on south aspects this layer sits above a crust. This layer will take time to adjust to the new snow load and warm temperatures and can produce large avalanches.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    Warm temperatures with moderate winds are encouraging the new snow to settle into a potentially reactive slab especially in wind loaded features. At lower elevations the new snow may become saturated and form loose wet avalanches.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    3–5
    A weak layer buried mid-December is still producing dangerous avalanches over a month after it was first buried. Particularly for slopes around treeline, there is a danger for a small avalanche to step down to this layer increasing the consequences.

Confidence

Fair - Freezing levels are uncertain

Weather Forecast

A second warm wet weather system will hit the coast on Sunday although a week ridge of high pressure will protect the interior from the brunt of this system and I expect the Purcells will see only light flurries or showers on Sunday. Warm temperatures and moderate to strong SW winds will persist through until Tuesday

Avalanche Summary

Parts of this region that see good amounts of snow/rain with warm temperatures are likely to see an active avalanche cycle. Areas that stay dry may not see natural avalanches, but human-triggered avalanches will still be possible. Avalanches ran in the region during and after the last major storm, typically running on the mid-January surface hoar layer.

Snowpack Summary

Between 10 and 20 cm of new snow fell in the last storm which I suspect is rapidly settling into a soft slab. This new snow sits above a moderately dense upper snowpack . A weak layer of surface hoar crystals lies buried between 35 and 50 cm below the surface. This "mid-January" weak layer has been responsible for most of the recent avalanche activity. While reports do indicate that this layer is starting to gain some strength and is becoming more difficult to trigger when ski-cutting small slopes, I suspect that we will see it produce avalanches through the weekend as the snow pack adjusts to the recent snowfall and continued warm temperatures. The mid-December surface hoar/crust layer is typically down 60-120cm below the surface. The reactivity of this deeper weak layer appears to be quite variable but snow pack tests indicate that it still has the potential to produce large avalanches in some areas. The layer appears to be the most reactive at and below treeline. The mid-Nov weak layer comprising facets can still be found near the bottom of the snowpack but has generally become inactive.

Regions covered