Avalanche forecast

Purcells

Apr 5 – 6, 2012Avalanche Canada
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Avalanche danger

Sat
Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    3–6
    Large cornices hang over most lee slopes. Cornices may become weak with daytime heating so pay attention to what's happening above you & bear in mind that cornice fall could initiate large avalanches failing on persistent weak layers.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–5
    Winds remained surprisingly light throughout Wednesday's storm. Watch for the odd slab near ridge top.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–4
    Periods of sun are expected Friday & the new snow will likely react quickly to the strong solar input, producing loose snow avalanches.

Confidence

Good

Weather Forecast

Cool dry air out of the north brings light convective flow to much of the province Friday & Saturday. Friday: Sunny periods in the morning give way to broken cloud in the afternoon. Expect the occasional convective burst of snow. No significant precipitation is expected. Ridge top winds light out of the west. Freezing level tops out around 1700 m. Saturday: Freezing level starts at the surface, climbs to 1400 m, then returns to the surface overnight. Sunday: Flow switches from north to south Saturday evening resulting in slightly warmer temps Sunday. Freezing level climbs to around 1600 m. Winds very light at treeline, light and variable at ridge top.

Avalanche Summary

Very soft slab avalanches to size 1 were being triggered naturally and by skiers. Explosive work produced avalanches to size 2 in the north of the region. A size 2.5 avalanche was observed in remote terrain near Malachite spire. Activity slowed down Thursday; preliminary observations are limited to sluffing in steep terrain. Avalanches releasing on the deeply buried mid-February surface hoar are becoming less likely. Avalanches may step down to the weak layer of facets or depth hoar on a crust that was buried in October. There was another report of a skier who propagated a size 3.0 avalanche on the weekend near Golden; the skier was fully buried and quickly rescued by their companions (the incident is attached to this bulletin).

Snowpack Summary

Wednesday's system produced around 30 cm of new snow in the north & 20 cm in the south. This snow was accompanied by light NW winds that formed very soft slabs in wind exposed terrain. The recent storms have added up to about a 125 cm of snow in the region. High freezing levels have consolidated this snow into a cohesive slab that may be propagated remotely. 125 cm now rests on top of a sun crust that was buried on March 27th on southerly aspects, and above wind affected surfaces that may be facetted on northerly aspects. Operators are reporting moderate shears on this interface. Cornices are reported to be very large and exist on most ridge lines. The mid-pack is well settled and strong. There is a weak layer of facets or depth hoar in shallower snowpack areas that may fail with initial warming of the snowpack. There is also a weak layer of of facets or depth hoar above a crust at higher elevations where there was already snow in October.

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