Avalanche Forecast

Issued: Jan 19th, 2021 4:00PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Wind Slabs and Persistent Slabs.

Avalanche Canada astclair, Avalanche Canada

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Strong winds have made triggering wind slab avalanches possible at upper elevations. Be careful in drifted areas and assess open slopes and rollovers where a weak layer may be preserved. 

Summary

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Tuesday night: Partly cloudy, scattered flurries bringing up to 5 cm of new snow, strong west winds, alpine temperatures around -12 C.

Wednesday: Mix of sun and cloud, isolated flurries with trace accumulations, light west winds, alpine high temperatures around -12 C.

Thursday: Mainly sunny, light northeast winds, alpine high temperatures around -14 C. 

Friday: Mainly sunny, light north winds, alpine high temperatures around -15 C.

Avalanche Summary

Recent strong west winds are expected to have formed wind slabs in lee features at upper elevations that may be possible to human trigger. On Sunday, observers reported human-triggered avalanches in wind-stiffened snow in the south of the region (check out the MIN reports here and here). Cornices may be reaching their breaking point and can act as triggers on slopes below. 

On Saturday, professional operators reported a small (size 1) avalanche releasing 40 cm deep on the Jan 11th surface hoar layer. Observers south of Valemount also reported reactivity on the surface hoar buried down 45 cm. They saw both shooting cracks and slab activity at 1700m on an easterly aspect. 

Since field observations in this region are limited, please consider submitting your observations to the Mountain Information Network. 

Snowpack Summary

Winds have varied in speed and direction from southwest to northwest over the past few days, and they have redistributed the 10-25 cm of snow that fell over the weekend into a tricky loading pattern. Ongoing snow and wind over the past week have contributed to notable cornice growth. 

40-60 cm of snow from the past week has buried a weak of layer of surface hoar that showed reactivity over the weekend from observers in the south of the region. There are few observations from the northern parts of the region, so the distribution and sensitivity to triggering of this layer is uncertain. This persistent weak layer is most suspect in sheltered, open slopes at and below treeline. Don't let decreasing winds and a clearing trend on Wednesday lure you into committing terrain. While the likelihood of triggering an avalanche is decreasing, the consequences of getting caught in one of these avalanches are significant. This presents a deceptive low probability/high consequence scenario that requires careful assessment.

A couple of older persistent weak layers exist in the mid to lower snowpack. The distribution of these layers is variable, but they follow a similar pattern to the layer discussed above. The upper layer from late December, down about 70-120 cm, consists of spotty surface hoar at shaded treeline and below treeline elevations. The lower layer from early December buried 150 cm deep consists of a combination of decomposing surface hoar with a crust and faceted snow. This layer is most prevalent in areas near Valemount. Observations from adjacent regions show increasingly unreactive results, suggesting a trend towards dormancy.

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Be aware of highly variable recent wind loading patterns.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid exposure to slopes that have cornices overhead.

Problems

Wind Slabs

An icon showing Wind Slabs

Recent snow accumulations ranging from 10-25 cm have been redistributed by strong west winds into wind slabs on lee features at upper elevations. Given the recent variability in wind direction, anticipate wind slabs across a wide range of aspects. Ongoing wind and snow over the past week have contributed to cornice growth. Cornice falls may trigger avalanches on the slopes below. 

Aspects: North, North East, East, South East, South, South West, North West.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

A weak layer of surface hoar buried Jan 11 may be found 40-60 cm deep on open, sheltered slopes near and below treeline. There is uncertainty in the distribution and sensitivity of this persistent slab problem across the region.  

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Jan 20th, 2021 4:00PM