Bulletin d’avalanche

Sea To Sky

Dec 26 – 27, 2020Avalanche Canada
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Danger d’avalanche

Mon
Tue
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

New snow and wind are forming touchy slabs in leeward terrain features. Be mindful of the potential for storm slab avalanches to step down to deeper weak layers, resulting in large and destructive avalanches.

Problèmes avalancheux

  • Persistent Slabs

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

    A couple problematic layers may be found around 50 to 120 cm deep, including weak layers of surface hoar and faceted grains above a hard melt-freeze crust. There remains potential for storm slab avalanches to step down to these layers, resulting in large and destructive avalanches.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    20 cm of new snow is forecast to fall by the end of the day Saturday ontop of extensively wind affected surfaces, crusts and wind slabs. These older wind slabs have been reactive to riders and may continue to be reactive particularly in steep convex alpine terrain where new snow has been wind loaded overtop.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Friday night: 5-10 cm new snow, wind easing moderate to light southwest, freezing level 700 m.

Saturday: 10-15 cm new snow, strong southwest wind, alpine temperature -6 C, freezing level 900 m.

Sunday: Clearing, light southwest to northwest wind, alpine temperature -6 C, freezing level 1200 m.

Monday: Sunny, moderate northwest wind, alpine temperature -4 C, freezing level 1200 m.

Avalanche Summary

Numerous wind slab avalanches were reported this week, triggered naturally and by riders at treeline and alpine elevations. Check out these MINs for a few examples: here, here and here.

A few large avalanches have been observed over the past week, running on buried weak layers (described in snowpack summary). Most occurred on north to east aspects in the alpine. A size 2.5 reported Thursday from a coastal glaciated area west of the Squamish river. It was on a southeast aspect, 100 m wide with crown depth 40-80 cm deep.

Snowpack Summary

5-10 cm of new snow is forecast to fall through the day Saturday, bringing storm totals to 15-25 cm. The new snow sits over hard wind slabs and wind scoured surfaces in exposed terrain, and a melt-freeze crust on solar aspects at upper elevations.

Two potential concerning weak layers may be present in the snowpack: 

  • The shallower layer, around 60 to 100 cm deep, includes feathery surface hoar crystals. This layer may be found in sheltered terrain features at treeline and lower alpine elevations but has been reported as spotty across the region. 
  • The more widespread weak layer includes sugary faceted grains that overlies a hard melt-freeze crust. This layer ranges in depth from 10 cm to 120 cm due to the wind scouring and loading the snow in different terrain features over the past two weeks. The layer has been reported as being widespread up to around 2000 to 2200 m. 

To date we have mostly seen sporadic avalanche activity on these layers, but they remain possible to trigger where they exist in the mountains.

The remainder of the snowpack is well-settled.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Recent new snow may be hiding windslabs that were easily visible before the snow fell.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.

Régions couvertes