Avalanche forecast

Purcells

Mar 18 – 19, 2014Avalanche Canada
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Avalanche danger

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

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–4
    There are a number of persistent layers in the mid to upper snowpack which have professional operators concerned. These layers, which include recently buried crusts and surface hoar, continue to produce large avalanches in many parts of the region.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–4
    Recent storm accumulations may take longer to bond due to the presence of buried surface hoar and crusts. Snow forecast for Wednesday afternoon will add to this existing storm slab.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    3–5
    The early February interface is variably reactive and has produced deep and destructive avalanches in a nearby region with recent solar warming. Possible triggers include cornice fall, thin spot triggering or solar warming.

Confidence

Fair - Forecast snowfall amounts are uncertain on Wednesday

Weather Forecast

Wednesday: Light snowfall becoming moderate overnight (up to 15cm) / Strong southwest winds / Freezing level at 1500mThursday: Light flurries / Moderate westerly winds / Freezing level at surfaceFriday: A mix of sun and cloud / Light northwest winds / Freezing level at surface

Avalanche Summary

On Monday explosives control produced several slab avalanches to size 2.5 with a couple reaching the size 3 range. Explosives control also produced cornice fall to size 2. In a nearby region with a similar snowpack a size 3 natural persistent slab avalanche was triggered by solar warming. The avalanche occurred on a south facing slope at 2100m and destroyed timber in the run out. On Tuesday explosives control in the north of the region triggered a size 2.5 deep persistent avalanche which failed on basal facets in unsupported, rocky terrain.

Snowpack Summary

Up to 45cm of settling storm snow exists and has been blown by strong winds into much deeper deposits in lee terrain. These recent storm accumulations overlie crusts on previously sun-exposed slopes and surface hoar in shaded terrain. Rain at lower elevations have saturated the snowpack and lower elevation surfaces may now exist as a refrozen crust. 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