Avalanche forecast

Purcells

Feb 21 – 22, 2014Avalanche Canada
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Avalanche danger

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

Don't let the improving weather fool you, conditions are very tricky and prime for human-triggered avalanches.The hazard will increase on south facing slopes on the first day of full sun.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    3–6
    This problem is surprising very experienced professionals and remains primed for human triggering. This meter deep slab has shown a propensity for remote triggering, a phenomenon that should become more prevalent as the slab gains cohesion.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–4
    Storm snow is being redistributed as wind slabs on lee terrain features. Primary wind directions have recently been SW through NW. Weak cornices are also a concern and have the potential to trigger large avalanches on the slopes below.

Confidence

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

Weather Forecast

Some light disturbance is expected for Saturday and Sunday as a ridge of high pressure builds. Clear, cold, and dry conditions are expected for Monday once the ridge of high pressure has established. Saturday: A mix of sun and cloud, light scattered flurries 0-1cm, treeline temperatures around -10C, ridgetop winds light NWSunday: A mix of sun and cloud, light scattered flurries 0-2cm, treeline temperatures around -15C, ridgetop winds light NWMonday: Clear and sunny, treeline temperatures around -13C, ridgetop winds light NW

Avalanche Summary

Natural avalanche activity is generally decreasing now that the storm has ended but we are still receiving reports of natural activity. Conditions are ideal for human triggering right now and we have received numerous reports of skier triggered avalanches, many of which have released quite deep in the snowpack. Several of these avalanches were remotely triggered. On Thursday, 2 remotely triggered avalanches and 1 skier controlled avalanche were reported in the Purcells. The largest of these was a size 2.5, the farthest trigger was 75m away, and the deepest was 80cm.  Early reports suggest an avalanche accident involving 1 or more people may have occurred on Friday near Golden.

Snowpack Summary

The recent ten-day storm has produced a cohesive slab that averages 40-90 cm in thickness. This slab sits on a nasty persistent weak layer (surface hoar/facet/crust combo) that was formed during the preceding month of cold, dry weather. This weak layer is widespread at all elevations and aspects, and is creating problems even in previously skied terrain. Large settlements and whumpfs have been reported at all elevations. We have received numerous reports of remotely-triggered avalanches from as far as 200m away which indicates a high likelihood of large propagations within the weak layer. We expect touchy conditions to remain in place longer than we're normally accustomed to. Recent strong winds out of the SW through NW have created wind slabs on leeward features in wind exposed areas at treeline and in the alpine. In many areas, thick wind slabs may overlie the persistent weak layer creating conditions for very large avalanches.Weak basal facets exist in some areas, but triggering has now become unlikely. For the most part, the mid and lower snowpack are strong and well consolidated.

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