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Avalanche Forecast

Archived

Dec 8th, 2021–Dec 9th, 2021

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
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 and human triggered avalanches likely.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Coast.

Pay attention to how the wind has drifted snow as you gain elevation. Areas with drifted snow over a crust may be reactive to human triggering, especially near ridges and roll-overs.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Wednesday night: Mainly cloudy, moderate west wind at ridgetop, isolated convective flurries with up to 5 cm of snow, freezing level near 800 m.

Thursday: Mostly cloudy, light northwest wind, isolated light flurries with trace accumulations, temperatures around -5 C near treeline, freezing level 500 m.

Friday: Cloudy, 5-15 cm of snow with an intense storm moving in overnight, moderate southwest wind gusting strong at ridgetop, temperatures rising to -3 C near treeline, freezing level rising to 700 m.

Saturday: Cloudy, 50-80 cm of snow expected to accumulate by mid-morning, strong southwest wind, temperatures rising to +2 C overnight during heaviest precipitation and dropping through the day, freezing level rising to 1100m and dropping to 500 m by end of day.

Avalanche Summary

No recent avalanche activity has been reported. 

Small loose dry avalanches were observed out of steep terrain on Monday.

Snowpack Summary

At upper elevations north in the region, 5-15 cm of snow has added to accumulations from earlier this week. Moderate southwest winds have likely redistributed available snow into dense wind slabs in wind-exposed areas. These wind slabs may be reactive to human triggering in immediate lee terrain features (for example, just down-wind of ridges), particularly where the snow is not well-bonded to the buried crust that formed during the last big rain event. 

We have a lot of uncertainty about the composition and reactivity of this widespread crust interface. There have been reports in the north of the region of surface hoar above the crust at upper elevations. Check out this MIN report from Sunday that shows these surface hoar crystals. As snow gradually accumulates and settles into a cohesive layer above it, we are vigilantly tracking this layer ahead of the incoming weekend storm. Send us your observations of what's above the crust where you are travelling using the Mountain Information Network. 

Last week's rainy atmospheric river event has eroded snow depths at and below treeline to below the threshold depth for avalanches.

Terrain and Travel

  • Be alert to conditions that change with elevation and wind exposure.
  • Wind slabs may be poorly bonded to the underlying crust.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

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.