Avalanche forecast

Purcells

Mar 16 – 17, 2014Avalanche Canada
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Avalanche danger

Tue
Wed
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

New snow combined with a complex snowpack means this is no time to be pushing into steep terrain. Conservative slope selection is critical to safe mountain travel.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–4
    Sunday's wind and snow has created a punchy storm slab which overlies a number of potentially weak surfaces. Forecast sunny breaks over the next few days will likely add to the reactivity of the new snow.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–4
    Rain at lower elevations has increased the likelihood of pushy loose wet avalanches in steep terrain. Loose wet avalanches (which may trigger deeper slabs) are also likely at higher elevations if solar radiation is strong.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–5
    There are now a few persistent weaknesses in the mid and upper snowpack which continue to produce very large natural avalanches. Forecast sunny breaks or the load of the new snow may spark ongoing destructive activity at all elevation bands.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Monday

Weather Forecast

Overview: A generally dry ridge of high pressure will develop on Monday and Tuesday with the passing of Sunday's frontal system. Another pulse will bring moisture to the region on Wednesday.Overnight Sunday: Up to 15cm of snow / Moderate to strong westerly winds / Freezing level at about 1500mMonday: Light flurries with the possibility of sunny patches / Moderate westerly winds / Freezing level at 1200mTuesday: Mix of sun and cloud / Light northwesterly winds with strong gusts / Freezing level at 1500mWednesday: Moderate snowfall / Moderate westerly winds / Freezing level at 1500m

Avalanche Summary

Although observations were limited on Saturday, a size 3 natural persistent slab avalanche was triggered on a south aspect in the north of the region. The avalanche is thought to have failed on a recently buried crust/surface hoar interface. With Sunday's storm, I expect avalanche activity to include a significant round of storm slab activity as well as continued destructive persistent slab activity.

Snowpack Summary

At the time of publishing up to 40cm of new snow had fallen and was blown by strong winds into much deeper deposits in lee terrain. Rain at lower elevations continued to saturate the snowpack. These recent accumulations overlie crusts on previously sun-exposed slopes and surface hoar in shaded terrain. More precipitation and wind forecast for Sunday night will add to this developing storm slab. Below the new snow, 60-100cm of settled snow has been bonding poorly to buried surface hoar and crusts. The deeper facet/crust persistent weakness buried at the beginning of February, now down 60 to 160cm, has been highly variable in terms of reactivity and is still very difficult to trust. Needless to say, any avalanche at these deeper, persistent interfaces would be large and destructive.Weak basal facets exist in many areas, but without a large load, triggering now is unlikely.

Regions covered