Avalanche Forecast

Archived

Dec 20th, 2023–Dec 21st, 2023

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural and human triggered avalanches likely.

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

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

Expect avalanche danger to rise to High through the day on Thursday. Snow, wind and warm temperatures are likely to overload a persistent slab problem.

Confidence

Moderate

Avalanche Summary

A remotely (from a distance) triggered size 2 persistent slab avalanche was reported on a north aspect at 1350 m on Tuesday. The fracture line was 50 cm deep and ran on a surface hoar layer 50 cm deep.

Additionally there were numerous naturally triggered size 2 persistent slab avalanches running on north aspects suspected to have run on surface hoar buried in early December.

Snowpack Summary

15-30 cm of new snow may accumulate Wednesday night through Thursday.

A buried layer of weak, feathery surface hoar crystals buried mid-December can be found down 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

Wednesday Night

Cloudy with snow 5-10 cm, ridgetop wind southwest 30 to 50 km/h, treeline temperature -3 °C, freezing level 900 m.

Thursday

Cloudy with 10-20 cm of snow, ridgetop wind southwest 30-60 km/h, treeline temperature -2 °C. freezing level 1100 m.

Friday

Cloudy with 10 to 20 cm of snow, ridgetop wind south 40-80 km/h, treeline temperature -2 °C, Freezing level 700 m.

Saturday

Cloudy with 1-3 cm of snow, ridgetop wind south 20-30 km/h, treeline temperature -4 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Storm slab size and sensitivity to triggering will likely increase through the day.
Minimize exposure during periods of heavy loading from new snow and wind.
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.

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.