Avalanche forecast

Sea To Sky

Dec 20, 2018Avalanche Canada
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Archived · expired 8 years ago

Avalanche danger

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

The danger will increase to HIGH, corresponding with Thursday's storm. It is a good day to avoid avalanche terrain and stick to sufficiently low-angled terrain and densely-spaced trees.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1.5–3.5
    Expect new snowfall to be reactive to human traffic. Deeper slabs will exist in lee terrain features due to strong south winds. It is possible that storm slabs could step down to deeper weak layers and produce very large avalanches.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

WEDNESDAY NIGHT: Cloudy with light snowfall, accumulation 5 to 10cm. THURSDAY: Cloudy with snowfall, accumulation 30 to 50cm, strong to extreme southwest winds, alpine temperature -1°c, freezing level rising from 1000 m to 1500 m over the day. FRIDAY: Partly cloudy, moderate west winds, alpine temperature -9°c, freezing level 600m. SATURDAY: Cloudy with light snowfall, accumulation 5 to 10cm, moderate southwest winds, alpine temperature -7°c, freezing level 600m.

Avalanche Summary

Many avalanches were triggered from skiers and explosives on Tuesday and Wednesday. Most of the avalanches were small to large (size 1 to 2) and released in the recent storm snow, 30 to 100 cm deep. Many of the avalanches were stepping down to older layers. Four very large avalanches (size 2.5 to 3.5) were triggered in the region with slabs around 100 to 200 cm thick and likely released on a weak layer near the base of the snowpack, as described in the snowpack discussion.Expect a similar trend of avalanche activity on Thursday with the incoming storm.

Snowpack Summary

About 3 m of snow has accumulated over the past 10 days. We are in the midst of another storm impacting the region on Thursday, which will bring more snow and strong to extreme southwest winds. Expect the new snow to be reactive to both skier activity and natural triggers.A weak layer of facets and surface hoar lies below all this storm snow. Recent avalanche activity is running in the storm snow above this layer but there have been reports of avalanche stepping down deeper within the snowpack, possibly to this weak layer.At the base of the snowpack, weak and sugary facets exist below an early-season melt-freeze crust. This weak layer has been the culprit for sporadic, very large avalanches in alpine terrain in the past few weeks. The avalanches have occurred in areas where the ground roughness is very smooth, for example glaciers, firn, and shale/rock slab slopes. An avalanche could be triggered in this layer in areas with smooth ground roughness either where the snowpack is thin or with a very large trigger such as a cornice fall. Storm slab avalanches could also step down to this layer.

Regions covered