Avalanche forecast

Sea To Sky

Apr 17 – 18, 2018Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

A warming trend is expected on Wednesday with possible sunny periods. This recipe recently produced large, destructive avalanches on a buried weak layer. Don't be complacent -- these are not typical spring snowpack conditions.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2
    Lingering wind slabs exist near ridges. They are found on all aspects due to winds starting from the north and then shifting to the south. Watch your overhead exposure, as cornice falls could trigger slabs on slopes below.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3.5
    Professionals are travelling cautiously due to a weak layer buried 60 to 140 cm. The layer is found in upper treeline and alpine terrain on shady aspects. Recent avalanches were triggered during sunny and warm weather, which may occur Wednesday.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2.5
    The sun packs quite a punch at this time of year. Be cautious if the sun comes out or if you feel warm air temperatures, as this will weaken the snow surface and increase the likelihood of loose wet avalanches.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

WEDNESDAY: Mostly cloudy with light snowfall and afternoon clearing, accumulation 1 to 3 cm, light southeast winds, alpine temperature -6 C, freezing level 1400 m.THURSDAY: Mostly sunny, light southwest winds, alpine temperature -5 C, freezing level 1600 m.FRIDAY: Cloudy with light snowfall, accumulation 2 to 5 cm, light to moderate southwest winds, alpine temperature -5 C, Freezing level 1500 m.

Avalanche Summary

On Monday, small slabs and loose wet avalanches were triggered by skiers and the sun.  The slabs were most often in lee terrain features near ridges.On Sunday, a large (size 3) persistent slab avalanche was remotely triggered by a snowmobile on a north aspect in alpine terrain after substantial air temperature and solar warming over the day.  The avalanche likely released on the weak layer described in the Snowpack Summary.  Another large avalanche was observed close to Whistler, on a north aspect around 2000 m, with a depth of about 1 m.  It was suspected to have released during last weekend’s storm followed by sun and likely on the same weak layer.  Be particularly cautious with this layer on Wednesday, as the sun may periodically shine along with rising freezing levels.

Snowpack Summary

10 cm of new snow has been redistributed from strong north winds followed by southwest winds.  This overlies variable surfaces, including old wind slabs at high elevations, a sun crust on south aspects, and a temperature crust on all aspects.  Ridgelines are heavily corniced and if they fail, they could trigger slabs on slopes below.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 60 to 140 cm. This layer is spotty in its distribution and has recently produced large and destructive avalanches. It is mostly likely to be problematic on west, north, and east aspects between 1900 m and 2250 m.  Professionals are treating it seriously and avoiding terrain because of it.Below this, the snowpack is well-settled and strong.

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