Avalanche Forecast

Issued: Jan 13th, 2021 4:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Storm Slabs and Persistent Slabs.

Avalanche Canada cgarritty, Avalanche Canada

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Ease into terrain cautiously on Thursday. Start small and tune in to signs of instability like shooting cracks and recent avalanches. Be mindful that sunshine can have a powerful effect on stability - and on your desire to push into aggressive terrain.

Summary

Confidence

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

Weather Forecast

Wednesday night: Diminishing cloud with isolated flurries. Light to moderate west wind, easing into the morning.

Thursday: Mainly sunny. Light west or northwest wind, increasing and shifting southwest in the afternoon, becoming extreme overnight. Alpine high temperatures around -7.

Friday: Cloudy with isolated flurries and a trace of new snow. moderate southwest winds. Alpine high temperatures around -7, freezing level rising to 900 m.

Saturday: Cloudy. Light to moderate south winds. Alpine high temperatures around -7.

Avalanche Summary

We're still awaiting field observations from the aftermath of Tuesday's storm, however it it's safe to assume it was a busy day for natural avalanches as up to 40 cm of new snow blanketed the region and was redistributed by strong winds. This activity was likely less pronounced in the north of the region, which saw closer to 15 cm of new snow.

Looking forward, expect Thursday to be another tricky day to be in the mountains, with new and reactive wind slabs formed in wind-exposed areas and even more widespread storm slabs primed for human triggering in more sheltered areas.

Field observations in this region are limited. If you get out, please consider submitting your observations to the Mountain Information Network. 

Snowpack Summary

15-40 cm of new snow fell in the region during Tuesday's storm, with accumulations greatly favouring the south of the region. This buried wind affected surfaces at upper elevations, as well as surface hoar in wind sheltered areas and a thin crust on solar aspects. 

The new snow will take time to form a bond with these previous surfaces, particularly in spots harbouring surface hoar or crust. In exposed areas, elevated winds have likely been redistributing new snow into reactive wind slabs and adding to cornices.

A couple of persistent weak layers exist in the upper to mid snowpack, down 20-60 cm and 70-100 cm. The distribution of these layers are variable, the upper layer spotty at treeline and below and the lower layer may present as decomposing surface hoar and/or a crust. It has been reported as most prevalent in areas near Valemount. 

Avalanche activity on these layers have dwindled since the last storm and recent snowpack tests results have been increasingly resistant, but still showing some propagation. Given their age (particularly the deeper layer) and the testing load brought by Tuesday's storm, the outlook is good for these layers to finally become dormant as our current surface instabilities diminish.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid exposure to steep sun exposed slopes.
  • Use small low consequence slopes to test the bond of the new snow.

Problems

Storm Slabs

An icon showing Storm Slabs

New snow and strong winds have created new slab problems that are likely to vary with elevation and wind exposure. In exposed areas, thick and reactive wind slabs should be expected in leeward features loaded by the wind. In sheltered areas, storm slabs are more likely to exist uniformly across all aspects and be particularly touchy where they overlie surface hoar. Both problems will be greatest in the southern half of the region.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

A couple of weak layers exist in the mid snowpack, buried 30-100 cm and 80-140 cm below the surface. They are highly variable in distribution and trending toward dormancy, but they are being tested by a new load of new snow. Some potential currently exists for avalanches in surface layers to step down to a deeper layer to create larger, even more destructive avalanches.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Jan 14th, 2021 4:00PM