Avalanche Forecast
Issued: Dec 22nd, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
MBender,
Avalanche Canada
50 to 80 cm of new snow from the past week rests on a variety weak layers. It is best to adopt a conservative approach to terrain selection as the snowpack adjusts the load.
Summary
Confidence
Weather Forecast
TUESDAY NIGHT: Broken cloud cover, moderate northwest wind, alpine temperature near -12 C.
WEDNESDAY: Scattered cloud cover, light to moderate west wind, alpine temperature near -6 C.
THURSDAY: Mainly sunny, light southerly wind, alpine temperature near -2 C with potential for a light alpine temperature inversion.
FRIDAY: Mix of sun and cloud, light southwest wind, alpine temperature near -5 C.
Avalanche Summary
Over the weekend a natural avalanche cycle took place with avalanches averaging size 1.5 to 2.5, but there were a few size 3 and even size 3.5's in the mix too. Many of the larger avalanches likely ran on persistent weak layers.
Snowpack Summary
60 to 100 cm of storm snow has fallen over the last week. Underneath this storm snow there is a sandwich of weak layers which are widespread throughout the region.
Just under the new snow, down about one meter below the surface is the mid December surface hoar. This layer has been failing naturally and has been quite sensitive to human triggering throughout the storm cycle. Large avalanches have been running on this interface connecting big terrain features.
Below that lies the early December persistent weak layer, it's about 80 to 140 cm below the surface. This weak layer is a mixed bag that often presents as surface hoar and facets sitting on top of a stout supportive crust. This is a nasty weak layer, when avalanches fail on it, they have been large and destructive. Smaller avalanches in motion can step down to this one too. This weak layer is going to haunt us for the foreseeable future.
Terrain and Travel
- Uncertainty is best managed through conservative terrain choices at this time.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Carefully manage your exposure to overhead hazards while entering and leaving riding areas.
Problems
Wind Slabs
There is lots of snow available for recent moderate to strong northwesterly winds to transport into alpine and treeline lee terrain.
Aspects: North East, East, South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
The last storm pushed the persistent slab problem over the tipping point resulting in very large avalanches Saturday & Sunday. The slab rests on a persistent weak layer which has the capacity to propagate avalanches across terrain features. Wind exposed features are expected to be particularly volatile.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 23rd, 2020 4:00PM
