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Avalanche Forecast

Archived

Apr 10th, 2023–Apr 11th, 2023

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Coastal, Kitimat, Nass, Rupert, Seven Sisters, Shames, Stewart, Howson, Ningunsaw.

Storm slabs will likely be reactive to human triggers; especially in wind-affected terrain and/or where the recently formed slabs are sitting on weak facets.

Choose conservative terrain and watch for clues of instability.

Confidence

Moderate

Avalanche Summary

A very large (size 3) explosive triggered a persistent slab avalanche on a west aspect in the alpine was reported on Monday.

On Sunday, explosive triggered persistent slabs up to size 3 were reported on primarily northerly aspects in the alpine. Additionally, a size 2 wind slab (40 cm deep) was triggered by a helicopter landing on a ridge. The avalanche occurred on a north aspect at treeline and sympathetically triggered three more avalanches below the ridge.

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

30-60 cm of recent snow fell dry above 1500 m and as rain below 700 m. At upper elevation, the new snow continues to be redistributed by southwest winds into wind slabs on north-to-east-facing slopes. The recent snow sits over wind-affected surfaces, weak faceted crystals or a crust on south-facing slopes.

A weak layer buried at the end of March sits 50-80 cm deep in most areas (potentially over 1m deep in immediate coastal terrain). It includes facets and surface hoar in shaded areas, and a melt-freeze crust elsewhere.

The mid and lower snowpack are considered generally strong and well-bonded. In 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

Monday night

Snow; 10-20 cm / 20 km/h south ridgetop wind / Temperature at treeline around -7 C / Freezing level valley bottom

Tuesday

Mostly cloudy with isolated flurries; 0-3 cm / 10 km/h west ridgetop wind / Temperature at treeline around -4 C / Freezing level 1000 m

Wednesday

Mix of sun and cloud / 10 km/h west ridgetop wind / Temperature at treeline around -6 C / Freezing level 900 m

Thursday

Cloudy with isolated flurries; 0-5 cm / 20 km/h south ridgetop wind / Temperature at treeline around -5 C / Freezing level 900 m

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Stick to simple terrain features and be certain your location isn't threatened by overhead hazard.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Avoid freshly wind loaded terrain features.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.