Avalanche Forecast

Archived

Dec 10th, 2021–Dec 11th, 2021

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

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

Cariboos.

New snow and wind are forming touchy slabs. Stick to simple terrain and be aware of what is above you at all times.

Confidence

High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

Friday night: 5-15 cm of new snow. Strong to extreme southwest wind. Freezing level climbing to 900 m.

Saturday: 10-20 cm of new snow. Strong southwest wind easing in the afternoon. Treeline temperatures around -8 C. Freezing level 800 m.

Sunday: 5-15 cm overnight then a mix of sun and cloud. Moderate southwest wind. Treeline temperatures around -10 C. Freezing level valley bottom.

Monday: Flurries with sunny periods. Moderate southeast wind. Treeline temperatures around -10 C. Freezing level valley bottom.

Avalanche Summary

While there have been no avalanches reported in the past few days, there was likely some avalanche activity in the alpine during Wednesday's storm. Wind slab avalanches remain a concern at treeline and alpine elevations.

There were two human triggered avalanches involving persistent weak layers earlier this week. One was a size 2 avalanche triggered in a north-facing bowl near Barkerville. This avalanche is suspected to have occurred on a 50 cm deep surface hoar layer. The other was triggered near McBride and released on a steep rocky slope near treeline (see this MIN report). The failure layer was likely an early season crust/facet layer.

Snowpack Summary

15-30 cm of new snow falls amid strong wind over previously wind affected surfaces at upper elevations.

Storms over the past week delivered a total of 20-40 cm on top of a few potentially concerning layers including isolated layers of surface hoar around treeline and a slippery crust below 1800 m.

An early season crust layer with some weak snow around it can be found 100-250 cm deep in the alpine. There is also evidence of a weak surface hoar layer 50 cm deep in the Barkerville area.

Terrain and Travel

Storm slab size and sensitivity to triggering will likely increase through the day.
Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
Be careful to keep storm day fever from luring you out into bigger terrain features.
Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.

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.