Avalanche forecast

Northwest Coastal

Apr 16 – 17, 2023Avalanche Canada
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Avalanche danger

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

Numerous large persistent slab avalanches have been triggered by riders during the past week.

Conservative terrain selection is critical, choose only well-supported, low-consequence lines.

Avalanche problems

  • Wind Slabs

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

    Recent snow and strong southeast wind have formed wind slabs on lee features at treeline and above.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–3

    Sunshine on Monday may increase the likelihood of triggering large persistent slabs.

    The primary concern is a layer of facets and surface hoar buried 50-90 cm on shaded slopes. On other slopes, this layer is a crust with facets above. Avoid steep open slopes capable of producing large avalanches.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–1.5

    Expect wet loose avalanches to begin releasing naturally when the sun heats up the recent snow.

Confidence

Moderate

Avalanche Summary

Numerous naturally triggered dry loose and wet loose avalanches up to size 1.5 were reported on sunny aspects on Saturday. Additionally, a naturally triggered size 2 wind slab avalanche was reported on a north aspect in the alpine.

Two persistent slab avalanches were reported northwest of Terrace last Wednesday. A skier triggered size 2 on a north aspect in the alpine and a size 2.5 on an east aspect in the alpine that was triggered by solar radiation. Both failed on a layer of weak facets and/or surface hoar down 40-50 cm.

A fatal avalanche occurred north of Stewart last Tuesday. It was a skier-triggered size 3 persistent slab avalanche that occurred on a northeast aspect in the alpine.

Two additional skier-triggered size 2-2.5 persistent slab avalanches were also reported on northerly aspects at treeline and above on Tuesday. The depth of the weak layer was around 60-80 cm.

Observations are limited at this time of year, please consider sharing any information or photos you have on the Mountain Information Network to help guide our forecasts.

Snowpack Summary

10-20 cm of recent snow and strong southeast wind have formed fresh wind slabs that may be reactive to human triggers on lee features at treeline and above.

Two buried weak layers are down 40-120 cm deep in most areas. They include facets and surface hoar in shaded areas, and a melt-freeze crust elsewhere. Numerous human triggered persistent slab avalanches have occurred on these layers this week.

The mid and lower snowpack are considered generally strong and well-bonded. In the far northern reaches of the region, basal facets may exist which are currently considered inactive. This layer may become active with abrupt changes to the snowpack, such as rapid loading (heavy snowfall or rain) or prolonged warming.

Weather Summary

Sunday Night

Partly cloudy with isolated flurries; 0-10 cm / 30 km/h south ridgetop wind / Temperature at treeline around -8 C / Freezing level valley bottom

Monday

Mostly sunny / 10 km/h east ridgetop wind / Temperature at treeline around -3 C / Freezing level 1200 m

Tuesday

Mix of sun and cloud / 20 km/h south ridgetop wind / Temperature at treeline around -3 C / Freezing level 1200 m

Wednesday

Mostly sunny / 20 km/h east ridgetop wind / Temperature at treeline around -2 C / Freezing level 1300 m

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Cornice failure may trigger large avalanches.
  • If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Regions covered