Avalanche Forecast
Issued: Dec 15th, 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 danger may be Moderate, but the presence of a persistent slab problem demands conservative terrain choices and disciplined backcountry travel techniques.
Avoid likely trigger spots such as steep, rocky slopes with a shallow or thin to thick snowpack.
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
WEDNESDAY NIGHT: Cloudy / Light, southwesterly winds / Low of -12 C / Freezing level surface.
THURSDAY: Mix of sun and cloud / Light, northwesterly winds / High of -6 C / Freezing level 200 m.
FRIDAY: Mix of sun and cloud / Light, westerly winds / High of -9 C / Freezing level surface m.
SATURDAY: Snow; 5-10 cm / Strong, southwesterly winds / High of -3 C / Freezing level 500 m.
Avalanche Summary
Check out this recent MIN report of a naturally triggered size 3.5 storm slab avalanche reported on Sunday near Mt. Pierce.
In the neighboring Sea to Sky region, we received recent reports of four large (size 2-2.5) explosive-triggered persistent slab avalanches failing on the early December crust/facet layer. These occurred on northwest and northeast aspects in the alpine.
Snowpack Summary
Recent snow and strong southerly winds formed wind slabs on lee features in open terrain that may remain reactive to human triggers.
The primary layer of concern in the snowpack is a crust down 50-100 cm that was formed in early December. This layer has a weak layer of small facets (sugary snow) above it that will result in large avalanches if triggered.
This has created a Persistent slab problem that is tricky to manage and likely to surprise riders who choose to ride steep, rocky slopes with a shallow or thin to thick snowpack.
It's tricky to manage because it's unlikely to trigger this layer on many slopes, but the consequence of triggering it is massive.
This scenario requires conservative terrain choices and disciplined backcountry travel techniques.Â
Terrain and Travel
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- 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.
- Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
- 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 50-100 cm near a crust layer that formed in early December. The persistent slab problem may be possible to human trigger. Avoid likely trigger spots such as steep, rocky slopes with a shallow or thin to thick snowpack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Recent snow and strong southerly winds formed wind slabs on lee features in open terrain that may remain reactive to human triggers.
Aspects: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 16th, 2021 1:00PM
