Avalanche Forecast

Issued: Jan 20th, 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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Conditions are more complicated than meets the eye. Wind-drifted snow and a buried weak layer warrant careful evaluation in specific areas.

Summary

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Wednesday night: Partly cloudy, light north winds, alpine temperatures dropping to -14 C.

Thursday: Mainly sunny, light north winds, alpine high temperatures near -12 C.

Friday: Mainly sunny, light north winds, alpine high temperatures near -14 C. 

Saturday: Increasing cloud, light variable winds, alpine high temperatures near -15 C.

Avalanche Summary

Recent strong winds have formed wind slabs in lee features at upper elevations that may be possible to human trigger. Over the last few days, operators in neighboring Glacier National Park reported several large (size 2-2.5) wind slabs releasing naturally on a variety of aspects. Cornices may be reaching their breaking point and can act as triggers on slopes below. 

On Monday and Tuesday, several operators in the region reported small (size 1-1.5) human-triggered avalanches releasing on a weak layer of surface hoar on north, east and southeast aspects at treeline and below treeline elevations. These avalanches were breaking 25-45 cm deep. Check out this MIN report for a helpful example of a remote-triggered avalanche on this layer.

Snowpack Summary

Recent strong winds built wind slabs in lee features at upper elevations over a variety of surfaces, including isolated surface hoar, sun crusts, and settling storm snow. Ongoing snow and wind over the past week have contributed to notable cornice growth. A new sun crust may be forming on steep solar aspects. 

50-70 cm of snow from the past week has buried a weak of layer of surface hoar that is likely to be preserved in sheltered, open slopes at and below treeline. Observers in the south of the region continue to report sudden results in the snowpack tests and shooting cracks on this layer. Don't let benign weather lure you into complacency. Recent avalanche activity demonstrates that this layer is likely to be reactive where it is preserved and that it warrants 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 120-190 cm deep consists of a combination of decomposing surface hoar with a crust and faceted snow. Snowpack tests on these layers show increasingly unreactive results, suggesting a trend towards dormancy. 

Terrain and Travel

  • Carefully evaluate steep lines for wind slabs.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid exposure to slopes that have cornices overhead.

Problems

Wind Slabs

An icon showing Wind Slabs

Strong winds have redistributed recent snow into wind slabs on lee features at upper elevations that may be possible trigger. 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, 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 possible to trigger on open, sheltered slopes near and below treeline. This weak layer can be found buried 50-70 cm deep. Recent avalanche activity demonstrates that this layer is likely to be reactive where it has been preserved.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Jan 21st, 2021 4:00PM