Bulletin d’avalanche

Sea To Sky

Dec 12 – 13, 2022Avalanche Canada
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Archivé · expiré 4 years ago

Danger d’avalanche

Wed
Thu
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Points saillants

Carefully assess the bond between recent snow and the underlying surface. Shifting winds have likely formed wind slabs on a variety of aspects. These slabs could be larger and more reactive where they overlie a weak layer of surface hoar.

Keep in mind that small avalanches have the potential to trigger deeper weak layers, resulting in large, consequential avalanches.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2.5

    Strong southerly winds during last week's storm have created deep deposits of wind slab near ridges and peaks.

    If northerly outflow winds pick up on Monday, fresh wind slabs may form anywhere there is powdery, dry snow available to be transported. Watch for changing conditions throughout the day and avoid freshly wind-loaded terrain.

    Wind slabs could step down to the mid-November weakness in the middle of the snowpack, resulting in large avalanches.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–2.5

    Soft facets on a crust about halfway down into the snowpack may become more sensitive to triggering with additional load from last week's storm. Small avalanches could step down to this layer resulting in large, consequential avalanches.

Confidence

Moderate

Avalanche Summary

On Saturday, numerous natural, skier, and explosive-triggered storm slab avalanches were observed, ranging from size 1 to 2. These avalanches occurred on a variety of aspects in the alpine and treeline.

Around the Whistler area on Friday size 1 to 2 soft storm slab avalanches were triggered with explosives, by skiers, and naturally. Interestingly, some explosives released size 2 on the mid-Nov crust down about 50cm and propagated around 50m wide.

Looking forward to Monday, the avalanche problem will likely be more confined to wind-loaded areas at upper elevations. Be cautious around these wind slabs as they may remain sensitive to human triggering and have the potential to trigger deeper weak layers, resulting in large avalanches.

Please keep sharing your observations via the MIN; it helps strengthen our information gathering!

Snowpack Summary

Surface: Around 20 to 30 cm of recent snow, but also at or near the surface you can find wind scoured, wind pressed, and of course wind slabs. In wind sheltered deep snow areas there could be as much as 70 cm storm snow accumulations.Upper-pack: on shaded terrain at all elevations large surface hoar (up to 10 mm) and generally unconsolidated snow. The upper snowpack consists of 20-50 cm of light but settling snow.Mid-pack: 50 cm down (maybe 70 to 100 cm in deep wind loaded areas) is a late November crust, with soft facets above. This is likely the critical snowpack weakness. Professionals are concerned about the possibility avalanches releasing at this deeper interface with the new snow load. So is Sofia (thanks for the MIN); I especially like her snowprofile photo!

Total snow depths remain low for early December with 90 to 140 cm at treeline and up to 200 cm in the alpine. Much of the below treeline elevation band is below the threshold for avalanches.

Weather Summary

Sunday night

Clear periods. Alpine temperatures drop to a low of -7 °C. Ridge wind northeast 15 km/h. Freezing level at valley bottom.

Monday

A mix of sun and cloud. Alpine temperature reach a high of -4 °C. Ridge wind northeast 10 km/h. Freezing level rising to 700 meters.

Tuesday

Cloudy with sunny periods. Alpine temperatures reach a high of -1 °C. Ridge wind north 10 km/h. Freezing level rising to 1000 meters.

Wednesday

A mix of sun and cloud. Alpine temperatures reach a high of 1 °C. Ridge wind north 10-20 km/h. Freezing level rising to 1000 meters. A weak alpine temperature inversion may develop.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • The best and safest riding will be on slopes that have soft snow without any slab properties.
  • Avoid freshly wind loaded terrain features.
  • Use caution above cliffs and terrain traps where even small avalanches may have severe consequences.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Régions couvertes