Avalanche forecast

Sea To Sky

Dec 3 – 4, 2012Avalanche Canada
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Avalanche danger

Wed
Thu
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–5
    New storm slabs and wind slabs have formed and are reactive. Natural avalanches are likely, and rider triggered avalanches are very likely; especially on lee slopes, gullies, and behind terrain features that have been wind loaded.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–6
    Typical trigger points include thin rocky areas. Although triggering is unlikely, failure at this persistent weakness could trigger a large destructive avalanche.

Confidence

Good

Weather Forecast

A broad upper trough remains offshore for the short term, while an embedded frontal system brings heavy amounts of precipitation, rising freezing levels and strong SW winds Tuesday. On Wednesday the flow will switch from SW to a more zonal westerly flow, and precipitation amounts will ease up.Tuesday: Freezing levels 1000 m falling to 500 m overnight, snow amounts 20-35 cm, ridgetop strong-extreme SW winds, alpine temperatures near -8.0.Wednesday/Thursday: Unstable onshore flow with fast moving systems allowing light-moderate amounts of precipitation. Strong ridgetop winds expected, and freezing levels 500-800 m

Avalanche Summary

On Sunday widespread natural avalanche activity was reported size 1.0-2.0. On Saturday a size 1.5 skier triggered avalanche occurred below treeline, running on a crust in a specific terrain feature. Explosive testing done produced several size 1-2 slab avalanches, initiating within the storm slab instabilities. Wider propagations have been seen from convex terrain, remote triggering is likely.

Snowpack Summary

The Sea to Sky Region has seen anywhere from 90-150 cm of storm snow over the past 5 days. Storm slabs and fresh wind slabs continue to build. I suspect the old weak snow surfaces (thin sun crusts, SH, surface facets) that developed early last week have been cleaned out in most places.  Below this, the mid-pack seems to be fairly settled, strong and possibly bridging instabilities that may exist deeper.Under the mid-pack (100-250 cm down) sits the early November facet/ crust persistent weakness. Recent snowpack testing done on an East aspect @ 2000 m have shown hard results with sudden collapse characteristics. Areas that are most susceptible to trigger this deep persistent weakness are from a shallow, thin and variable  deposition spots. The continuous loading provides direct testing on the early November facet/crust weakness.

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