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Avalanche Forecast

Archived

Dec 11th, 2021–Dec 12th, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
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.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Cariboos.

Storm slabs will remain most reactive where wind has loaded deeper deposits onto leeward slopes. Raise your guard as you transition into wind-affected terrain.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength. Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Saturday night: Around 5 cm of new snow with local enhancements possible in the south. Moderate southwest wind. Freezing level valley bottom.

Sunday: A mix of sun and cloud, no significant precipitation. Light to moderate southwest wind. Treeline temperatures around -11 C.

Monday: A mix of sun and cloud with isolated flurries. Moderate southeast wind. Treeline temperatures around -8 C.

Tuesday: A mix of sun and cloud. Light southwest wind. Treeline temperatures around -12 C.

Avalanche Summary

We are still awaiting observations of avalanche activity during the storm.

There were two human triggered avalanches involving persistent weak layers last 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

The convective nature of yesterday's storm has resulted in highly variable snowfall amounts throughout the region. Generally, 10-25 cm of new snow from Saturday's storm has seen redistribution by strong wind at upper elevations.

A few potentially concerning layers exist in the mid to lower snowpack. A surface hoar layer observed near Barkerville, and a widespread crust below 1800 m both now sit 40-70 cm deep. An early season crust layer with some weak snow around it can be found 100-250 cm deep in the alpine.

Terrain and Travel

  • Start with conservative lines and watch for clues of instability.
  • Stay off recently wind loaded slopes until they have had a chance to stabilize.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.