Avalanche forecast

Sea To Sky

Dec 27 – 28, 2020Avalanche Canada
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Avalanche danger

Tue
Wed
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Watch for wind loading in atypical terrain features due to recent shifting wind. Expect cornices and storm slabs to remain reactive to human triggers especially if the sun comes out Sunday.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    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

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–2

    15-30 cm of recent snow has been redistributed by wind blowing from the east as it fell Saturday. On Sunday, storm slabs will likely remain most reactive in wind loaded lees such as below ridge crests and roll overs. New snow may become increasingly sensitive to triggering when touched by the sun for the first time.

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Saturday night: 5 cm new snow, strong southwest wind, freezing level 700 m.

Sunday: Mostly cloudy, light southwest wind, alpine temperature -5 C, freezing level 1000 m.

Monday: Sunny, light northwest wind, alpine temperature -5 C, freezing level 1000 m.

Tuesday: Increasing cloud, wind increasing to moderate southwest, alpine temperature -5 C, freezing level 500 m.

Avalanche Summary

Storm slabs and cornices were reported to be touchy during the storm on Saturday, skier end explosive control work producing storm slab avalanches size 1-2. Earlier this week, numerous wind slab avalanches were reported, 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

15-30 cm of recent snow has been redistributed by strong easterly winds, depositing deep pockets of storm slab into lee terrain features.

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

  • Be carefull around freshly wind loaded features.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Brief periods of sun could quickly initiate natural avalanche activity.
  • Conditions may have improved, but be mindful that deep instabilities are still present.

Regions covered