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Avalanche Forecast

Archived

Apr 11th, 2023–Apr 12th, 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 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.

Regions

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

Storm slabs will likely remain 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 signs of instability.

Confidence

Moderate

Avalanche Summary

Several skier and helicopter remotely triggered size 2 storm slabs were reported on a variety of aspects at treeline and above on Monday. The slabs were 25-80 cm thick.

Additionally, a very large (size 3) naturally triggered wind slab was reported on a northeast aspect in the alpine.

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

The recent storm produced 30-60 cm of snow (above 1500 m) and rain below 700 m. At upper elevations, southwest winds formed 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

Tuesday night

Partly cloudy / 10 km/h northwest ridgetop wind / Temperature at treeline around -7 C / Freezing level valley bottom

Wednesday

Mix of sun and cloud / 20 km/h west ridgetop wind / Temperature at treeline around -6 C / Freezing level 800 m

Thursday

Mostly cloudy with isolated flurries; 3-10 cm / 20 km/h southwest ridgetop wind / Temperature at treeline around -4 C / Freezing level 1000 m

Friday

Cloudy with isolated flurries; 0-5 cm / 30 km/h south ridgetop wind / Temperature at treeline around -3 C / Freezing level 1100 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.