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Avalanche Forecast

Dec 14th, 2021–Dec 15th, 2021
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Sea To Sky.

The current persistent slab problem is best managed through conservative terrain choices and disciplined backcountry travel techniques.

Avoid likely trigger spots such as steep, rocky terrain, with a shallow or thin to thick snowpack.

Confidence

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

Weather Forecast

TUESDAY NIGHT: Mostly cloudy / Moderate, southwesterly winds / Low of -9 C / Freezing level surface.

WEDNESDAY: Cloudy with isolated flurries; 0-3 cm / Moderate, southerly winds / High of -5 C / Freezing level 700 m.

THURSDAY: Mix of sun and cloud / Light, northwesterly winds / High of -5 C / Freezing level 400 m.

FRIDAY: Mix of sun and cloud / Light, northwesterly winds / High of -7 C / Freezing level 300 m.

Avalanche Summary

Several human triggered persistent slab avalanches up to size 2, failing on the early December crust were reported on Monday. See one example in this MIN report.

Snowpack Summary

Large amounts of recent snow and strong southerly winds have formed deep wind slabs on lee features in open terrain.

Pay attention to conditions that change with exposure to wind and monitor for cracking or drum-like sounds.

An impressive storm over the weekend brought 40-70 cm of new snow to the mountains with strong southwest winds. Below the storm snow (down 60-100 cm), there is a layer of weak facets (sugary snow) above a crust that formed in early December. 

Over the weekend, snowpack tests at upper treeline elevations produced sudden results at this interface (see this, this, and this MIN report). On Sunday, operators reported large, explosive-triggered avalanches releasing on this layer in alpine start zones. This persistent slab problem warrants careful evaluation and conservative route-finding as the recent snow consolidates into a more cohesive slab over the weak layer.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Cornice failures could trigger very large and destructive avalanches.
  • Uncertainty is best managed through conservative terrain choices at this time.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

Avalanche Problems

Persistent Slabs

A layer of weak facets (sugary snow) can be found down 60-100 cm near a crust layer that formed in early December. The persistent slab problem has demonstrated recent instability, and it may be possible to human trigger.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 3

Wind Slabs

Fresh wind slabs will likely form on lee features at treeline and above on Wednesday which may be reactive to human triggers.

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

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 2