Avalanche forecast

Purcells

Apr 6 – 7, 2012Avalanche Canada
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Archived · expired 14 years ago

Avalanche danger

Sun
Mon
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
    Cornices have grown large & unruly. Cornices receiving direct sun will eventually grow weak & there is potential for cornice fall to initiate deep persistent slab avalanches on underlying slopes. Pay attention to what's happening above you.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    2–6
    Two layers to watch: April 3rd, down 30 cm & Mar. 26, down 100 cm. I'd be wary of triggering the deeper layer on steep unsupported slopes, especially in places where the snowpack goes from thick to thin; near ridge crests and rock outcroppings.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–5
    Periods of sun are expected Saturday & the new snow will likely react to the strong solar input, producing loose snow avalanches, with the potential for deeper slab avalanches on slopes that bake all day under the strong spring sun.

Confidence

Fair - Timing or intensity of solar radiation is uncertain for the entire period

Weather Forecast

A stagnant weather pattern dominated by a ridge of high pressure brings increasingly sunny periods with benign convective cloud over the holiday weekend. Saturday: Freezing level starts at the surface, climbs to 1800 m, then returns to the surface overnight. Ridge top winds light out of the west, gusting to moderate in the afternoon. Sunday: Flow switches from north to south late in the day allowing freezing levels to climb all the way to 2000 m. Winds light East, switching S, SE Sunday night. Monday: Winds light S. Freezing level starts around 1000 m, climbs to 2000 m in the afternoon.

Avalanche Summary

Control work Thursday produced touchy soft slab avalanches up to size 2 that were intentionally triggered by both skiers and explosives. Widespread sluffing out of steep terrain was also observed. The sun came out in parts of the region Friday which no doubt initiated some avalanche activity. 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 40 cm of new snow in the north & 25 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.

Regions covered