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Avalanche Forecast

Archived

Dec 9th, 2021–Dec 10th, 2021

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

Regions

Cariboos.

Danger will increase throughout the day with the approaching storm. Pay close attention to changing conditions, especially at higher elevations.

Confidence

Moderate - Uncertainty is due to the complexity of the snowpack’s structure.

Weather Forecast

A frontal system will arrive on Friday night and bring strong wind and new snow.

THURSDAY NIGHT: Mostly cloudy, no significant precipitation, moderate wind from the west, treeline temperatures around -12 C.

FRIDAY: Increasing cloud with afternoon flurries bringing up to 5 cm of snow, strong wind from the southwest with gusts to 70 km/h, treeline temperatures increase to -8 C.

SATURDAY: Snowing throughout the day with a total of 15-25 cm, strong wind from the south with gusts to 90 km/h, treeline temperatures around -5 C.

SUNDAY: Mix of sun and cloud, no significant precipitation, light to moderate wind from the south, treeline temperatures around -8 C.

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

Storms over the past week delivered a total of 20-40 cm of new snow. The snow at higher elevations has been heavily wind affected, with scoured surfaces on windward terrain and wind slabs on leeward terrain. There are a few potentially concerning layers underneath the recent snow including isolated layers of surface hoar around treeline and a slippery crust below 1800 m. Regardless of the elevation, be alert to areas where the recent snow feels stiff or slabby.

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

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Caution around convexities or sharp changes in terrain.
  • Avoid areas where the snow feels stiff and/or slabby.
  • Be alert to conditions that change with elevation and wind exposure.

Problems

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.

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.