Avalanche Forecast
Issued: Dec 14th, 2021 1:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
JSmith,
Avalanche Canada
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.
Summary
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.Â
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.
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
Expected Size
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
Expected Size
Valid until: Dec 15th, 2021 1:00PM
