Avalanche Forecast
Issued: Dec 24th, 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
The load sitting on a variety of buried weak layers recently reached a tipping point. If triggered, avalanches running on these weak layers will likely be large and destructive. Continue to choose conservative terrain in the coming days.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
THURSDAY NIGHT: Clear periods, light southwest wind, alpine temperature near -8 C.
FRIDAY: Mix of sun and cloud, light southwest wind, alpine temperature near -5 C.
SATURDAY: Scattered flurries, accumulation 5-10 cm. light southwest wind, alpine temperature near -7 C.
SUNDAY: Mainly cloudy with sunny breaks, light west wind, alpine temperature near -8 C.
Avalanche Summary
On Wednesday there was a report of several size 3 to 4 explosives controlled deep persistent and persistent slab avalanches in the north of the region along the Highway 1 corridor. These ranged from south and east aspects to northeast running from the alpine to the valley floor.
Reports on Tuesday show a widespread storm slab and persistent slab avalanche cycle in the alpine and at treeline. Avalanches sizes ranged from size 1.5 to 3 on all aspects. Additionally reports from Tuesday in Rogers Pass indicate several natural and explosives controlled persistent slab avalanches to size 3.5-4 running full path from the alpine to the valley floor Monday night.Â
On Monday there were several reports of persistent slab avalanches running size 2.5 to 3 at treeline and in the alpine on east and west aspects.
Snowpack Summary
60 to 100 cm of snow fell 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 had 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.Â
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 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.
Terrain and Travel
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Remote triggering is a concern, watch out for adjacent and overhead slopes.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Uncertainty is best managed through conservative terrain choices at this time.
Problems
Wind Slabs
Wind switching directions has created wind slabs on a variety of aspects
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Recent storms have pushed the persistent slab problem over the tipping point resulting in very large avalanches. A slab rests on two persistent weak layer which has the capacity to propagate avalanches across terrain features.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 25th, 2020 4:00PM
