Avalanche Forecast

Archived

Dec 31st, 2024–Jan 1st, 2025

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 possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Northwest Coastal, Boundary, Kitimat, Nass, Rupert, Seven Sisters, Shames, Stewart, Howson, Microwave-Sinclair, Ningunsaw, Ningunsaw, Ningunsaw.

A problematic weak layer has been producing large, hair-triggered avalanches. Careful snowpack evaluation, cautious route-finding and conservative decision-making are critical.

Confidence

High

Avalanche Summary

Large to very large (size 2-4) natural and remotely-triggered persistent slab avalanches have been reported in recent days. Slabs have shown propagation as wide as 1 km and remote triggers as far away as 1km!

A couple of MIN reports from South Douglas on the weekend paint the picture: This sobering near miss surprised riders as a fracture line wrapped around a feature and this MIN describes skiers triggering large avalanches from valley bottom.

Snowpack Summary

Extensively wind-affected surfaces exist in the alpine. Soft snow at lower elevations will likely be redistributed as outflow winds pick up this week. Below 1000 m, surface snow is moist and/or crusty.

50 to 100 cm of snow sits over a significant weak layer. The layer involves weak grains of surface hoar and facets sitting over a crust. This layer has been the failure plane for recent large avalanches with wide propagation.

The remainder of the snowpack is well settled and bonded. Treeline snow depths are around 160 cm.

Weather Summary

Tuesday night

Partly cloudy. 10 to 30 km/h east outflow winds. Treeline temperature -12 to -16 °C.

Wednesday

Sunny. 20 to 40 km/h east outflow winds. Treeline temperature -12 to -16 °C.

Thursday

A mix of sun and cloud with isolated flurries bringing up to 5 cm. 40 to 60 km/h east outflow winds. Treeline temperature -13 to -17 °C.

Friday

A mix of sun and cloud with isolated flurries bringing up to 5 cm. 20 to 40 km/h east outflow winds. Treeline temperature -10 to -14 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Be aware of the potential for large avalanches due to buried weak layers.
Remote triggering is a concern; avoid terrain where triggering overhead slopes is possible.
Use conservative route selection and resist venturing into complex terrain.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

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.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.