Avalanche forecast

South Rockies

Mar 19 – 20, 2012Avalanche Canada
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Avalanche danger

Wed
Thu
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–6
    Wind slabs can be found behind ridges and terrain breaks. Large cornices also threaten slopes below.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–6
    New snow will continue to build storm slabs. Storm snow may release naturally with the first blast of sun. It's possible for surface avalanches to step down to a weak persistent layer, initiating large destructive avalanches.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    4–8
    Persistent weak layers, now buried 1-2m deep, still have the potential to produce large and dangerous avalanches. They could be triggered by cornice fall, smaller avalanches stepping down, and under the weight of a snowmobile and rider.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Tuesday

Weather Forecast

Another Pacific frontal system begins to track inland from the Coast late tonight into Tuesday. This will bring more snow, wind and rising freezing levels. Tuesday: Snow amounts near 5 cm overnight, another 10-15 cm during the day. Ridgetop winds strong from the West. Treeline temperatures near -2. Freezing levels 1100-1300 m. Wednesday: Convective weather pattern, cloudy with flurries. Ridgetop winds through the day up to moderate from the West. Treeline temperatures near -5. Freezing levels valley bottom. Thursday: Moderate to heavy snow amounts expected. Ridgetop winds strong from the SW. Freezing levels may spike up to 1300 m.

Avalanche Summary

No new reports on Monday. On Sunday, a size 1.5 avalanche released naturally on a north aspect. On Saturday, a recent avalanche was observed on a north aspect in the southern Elk Valley, suspected to have started as a wind slab and ending in moist snow. Evidence of a previous natural cycle was also reported. On Friday, explosives produced size 1-2 avalanches.

Snowpack Summary

Unsettled weather has brought snow and wind through most of the week, creating variable wind slabs and storm slabs. On Saturday, snowpack tests in the Elk Valley, east of Sparwood, showed a couple of shears in the top 20cm of storm snow. A rain crust is buried about 1m down. Two surface hoar layers, buried in February and now 1-2m deep, exhibited sudden planar results, which have been repeated in a number of locations. This means they still have the potential to produce widely-propagating, destructive avalanches if triggered. Most likely triggering mechanisms are a person traveling on a thin snowpack area, or a storm slab, wind slab or cornice stepping down. Basal facets may still exist, particularly in shallow snowpack areas with steep, rocky start zones. Cornices have grown large and threaten slopes below.

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