Avalanche forecast

Sea To Sky

Mar 16 – 17, 2017Avalanche Canada
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Avalanche danger

Sat
Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Fresh storm snow will be touchy in wind affected terrain on Friday, while another wet storm is lined up to increase the danger this weekend.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–4
    A weak layer down around 1 metre is creating a low probability/high consequence scenario. It is unlikely to directly trigger this layer but a small avalanche or cornice fall could still step down to it.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–2
    New snow will form fresh storm slabs that will be extra thick and touchy in wind loaded terrain. These slabs may bond poorly to the underlying rain crust. Cornices are also reported to be large and may still be weak.

Avalanche Summary

On Wednesday, evidence of a recent widespread natural avalanche cycle was reported, including numerous size 2-3 storm slabs and cornice failures. A few avalanches likely stepped down to deeper weak layers including the mid-February crust. Initial reports of explosive avalanche control on Thursday include up to size 2 cornice releases and several size 1.5 storm slabs. Ski cutting also produced smaller size 1 slabs. These avalanches failed at the interface between the new snow and rain crust and were up to 50 cm deep on wind loaded features.With more snow and wind in the forecast, expect fresh storms slabs to be reactive to human triggers on Friday. It has become difficult to trigger the mid-February crust/facet layer but there is still a chance that small storm slab avalanches or cornices could step down and release a persistent slab avalanche.

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Saturday

Weather Forecast

THURSDAY NIGHT: 10-15 cm of new snow with strong southwest winds.FRIDAY: Isolated flurries before the next storm arrives Friday evening, strong southwest winds, alpine temperatures around -8 C.SATURDAY: Storm starts Friday night and delivers about 30 cm, strong southwest winds, freezing level around 1000 m with alpine temperatures up to -5 C.SUNDAY: Clearing skies following the storm as alpine temperatures drop to around -10 C, moderate west winds.

Snowpack Summary

By Friday morning expect 20-30 cm of recent snow sitting above a widespread layer of wet snow up to about 2200 m. The wet snow layer is likely turning into a crust and may become a weak layers as storm snow accumulates. Strong south winds are likely forming thicker slabs in the lee of exposed terrain. The mid-February crust/facet layer is now typically down 80-120 cm and in wind loaded terrain, it may be as deep as 200 cm. With a thick layer of weak faceted snow above it, this crust layer was producing easy, sudden results in snowpack tests prior to the warming event. The layer is expected to gain strength with the cooler temperatures but there is a lot of uncertainty as to how long this layer will remain reactive.

Regions covered