Avalanche forecast

Sea To Sky

Nov 23 – 24, 2011Avalanche Canada
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Avalanche danger

Fri
Sat
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

Avalanche danger is expected to increase as another intense storm hits the coast.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–5
    Near ridgecrests and terrain breaks, and in cross-loaded gullies. Wind slab avalanches can be especially large and destructive.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    3–6
    Particularly touchy where there is an associated rain crust, which is prominent between 1800m and 2050m. Potential for remote triggering means that even low-angle terrain may not be safe if there is exposure from above.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–4
    Any open slope with enough snow to smooth out ground roughness. Fluctuating freezing levels created a weak 'upside-down' storm snow structure.

Confidence

Poor - Due to limited field observationsfor the entire period

Weather Forecast

Thursday: Snow starting mid-morning and increasing throughout the day with 10-20cm possible by late afternoon. Freezing levels around 900m and strong to extreme southeasterly winds shifting to westerlies and easing off in the evening.Friday: Mostly cloudy with flurries bringing 3-5cm. Freezing levels around 500m, and strong northwesterly winds becoming westerlies late in the day.Saturday: A warm intense Pacific frontal system brings heavy precipitation, extreme winds, and freezing levels possibly into alpine elevations.

Avalanche Summary

Recent reports confirm a widespread destructive natural avalanche cycle during the intense storm overnight Monday. More recent human-triggered whumpfing and large remote avalanches were reported to be associated with the mid-pack crust/facet complex at upper treeline and lower alpine elevations.

Snowpack Summary

Newly formed surface hoar is now buried by 50-70cm of recent storm snow. A persistent weakness of facets, with an associated crust at upper treeline elevations, can be found down 70-150cm. This weakness seems to be particularly touchy between 1800 and 2000m where it is very sensitive to human triggers and has a high propensity to propagate fractures. Buried surface hoar has also been spotted just below this crust, and sitting on top in some locations. A deeper crust with associated facets and/or depth hoar is approximately 50cm off the ground.

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