Avalanche forecast

Sea To Sky

Dec 4 – 5, 2012Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    2–5
    Fresh wind slabs can be found well below ridge crests, behind terrain features and in cross-loaded gullies in any wind-exposed terrain. Expect these deep drifts to be very touchy.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–6
    An old facet/crust combination deep in the snowpack may wake up with heavy triggers, smaller avalanches stepping down, or triggering from thin-spots, particularly on slopes with smooth ground cover.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–5
    Weaknesses within and under the recent storm snow are susceptible to human triggers, particularly in sheltered areas treeline and below, and could easily produce avalanches large enough to bury a person.

Confidence

Fair - Due to limited field observations for the entire period

Weather Forecast

Wednesday: Moderate snowfall in the morning and afternoon 5-10cm of accumulation for the day, freezing levels around 700m, and strong southwesterly mountaintop winds. Thursday: Moderate snowfall with 10-20cm of accumulation, freezing levels around 700m, and strong southwesterly winds becoming moderate westerlies. Friday: Light snowfall with a couple of centimeters of accumulation, freezing levels around 600m and moderate westerly winds.

Avalanche Summary

Reports from the Whistler area on Monday include numerous explosive-triggered and ski cut 20-100cm deep Size 1.0-2.0 storm slab and wind slab avalanches on northwest through east facing treeline and alpine slopes. One 50-150cm deep Size 2 slab avalanche may have stepped-down to the early November deep persistent weakness.

Snowpack Summary

Treeline and alpine areas have received well over a metre of new snow since late last week with weaknesses lingering within and under this storm snow. Of particular note was preserved 8mm surface hoar found on a sheltered open slope just below treeline, which gave moderate but energetic sudden collapse results in repeated compression tests. The mid-pack seems to be fairly settled, strong, and possibly bridging instabilities that may exist deeper. However, snowpack tests continue to produce  occasional hard but sudden results on the early November facet/crust combination down as deep as 200cm on leeward slopes. Furthermore, favorable slab structure for step-down fractures can contribute to the persistence of this deep weakness.

Regions covered