Avalanche Forecast

Archived

Dec 21st, 2023–Dec 22nd, 2023

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

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, human triggered possible.

Regions

Kitimat, Nass, Rupert, Seven Sisters, Shames, Howson.

Keep decision making conservative in the wake of the storm. Storm snow needs time to stabilize and buried weak layers will be sensitive to this new load

Stick to simple and supported terrain

Confidence

Moderate

Avalanche Summary

On Thursday numerous size 2 wind slabs were reported, naturally and human triggered. We expect widespread natural activity occurred on Friday as the wind and snow continued.

Several slab avalanches up to size 2 have been reported this week on the buried surface hoar layers, primarily on north facing slopes around treeline. These reports include natural and remote human triggers.

Snowpack Summary

30-60 cm of new snow will have fallen by midday Friday, with strong winds creating deeper deposits in north and east facing terrain.

A buried layer of weak surface hoar buried mid-December can be found 35 to 60 cm from the surface. An additional layer of buried surface hoar may exist deeper in the snowpack, roughly 70 to 100 cm below the surface.

The remaining mid and lower snowpack contains several crusts from early in the season that are generally well-bonded to the surrounding snowpack. Snow depth decreases significantly at lower elevations.

Weather Summary

Thursday Night

Cloudy with another 20-30 cm of snow possible, favouring coastal areas as usual. Winds strengthen to 60-80 km/h from the south. Freezing levels sit around 1000 m.

Friday

Cloudy with 10 cm of snow, southerly winds 40-60 km/h, treeline temperature -2 °C. Freezing level 700 m.

Saturday

Cloudy with 1-3 cm of snow, southerly winds increase, 60 km/h. Freezing levels rise over the day to 1500 m treeline temperature -1 °C.

Sunday

Cloudy with light snowfall. Freezing levels rise to 1500 m, and southerly winds strengthen to above 100 km/h.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
Storm slabs in motion may step down to deeper layers resulting in large avalanches.
Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.

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.