Avalanche Forecast
Issued: Dec 1st, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Deep Persistent Slabs and Loose Wet.
swerner,
Avalanche Canada
The snowpack doesn't respond well to rapid change. The impact of the afternoon sun and warm temperatures could bump up the avalanche danger to HIGH. Watch for signs of instability and be conservative with your terrain selection.
Summary
Confidence
Weather Forecast
Wednesday: Sunny with some cloudy periods. Ridgetop winds 15-25/h km from the south and alpine temperatures + 8 degrees. Freezing levels 3500 m.
Thursday: A mix of sun and cloud. Ridgetop winds 10-20 km/hr from the southwest and alpine temperatures near + 4 degrees. Freezing levels 3000 m.
Friday: A mix of sun and cloud. Ridgetop winds 15-30 km/hr from the southwest and alpine temperatures + 5 degrees. Freezing levels 3000 m.
Avalanche Summary
On Tuesday, a large size 3 natural avalanche was observed on a NE aspect at 2400 m. It was reported as a cornice failure triggering the slope below and appeared to have slid on the early November crust near the base of the snowpack.
On Wednesday, we may see more of these deeper releases with the warm up as well as smaller natural avalanches becoming especially reactive where recent snow sits over a crust or surface hoar. Loose wet avalanches are also likely.
Our eyes and ears in the mountains are limited at this time of year and may continue this winter due to fewer professional observations. If you see anything (or don't) while out in the field, please consider sharing via the Mountain Information Network (MIN). Photos are especially helpful! Thank you so much for all the great MINs submitted so far!
Snowpack Summary
10-20 cm of recent snow has been wind loaded into lee features in exposed areas at upper elevations and may sit over a thin melt-freeze crust on south aspects and possibly surface hoar in wind-sheltered areas around treeline. Forecast sun and rising freezing levels into the alpine will have the greatest impact on the upper snowpack, showing signs of instability.
The lower snowpack is characterized by a few crusts formed during warm periods over the last month.
- In the north, treeline snowpack depth sits around 80 to 120 cm. The crust of note here is sitting near the base of the snowpack, likely surrounded by a weak layer of sugary facets. Snowpack tests and recent avalanche activity suggest that this layer could be triggered by humans and produce large avalanches.
- In the south of the region, the snow line has been reported around 700 m near Hope and treeline snowpack depth sits around 100-150 cm. The deeper crusts in this area are generally well bonded to surrounding snow.
Terrain and Travel
- The likelihood of deep persistent slab avalanches will increase with each day of warm weather.
- Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
- Avoid steep slopes when air temperatures are warm, or solar radiation is strong.
Problems
Storm Slabs
A sharp rise in temperature coupled with solar radiation on will promote rapid settlement and accelerated slab development in the recent storm snow. Be especially cautious where new snow may sit over a crust (south aspects) or surface hoar (wind sheltered areas around treeline).
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
In the north of the region (e.g., Duffey Lake), a weak layer of sugary faceted grains around a hard melt-freeze crust sits near the base of the snowpack. Avoid slopes with overhead hazards like cornices. If they fail during the warm-up they could trigger the slope below.
This problem does not exist in the south of the region.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
A rapidly warming snow surface may release loose wet avalanches. Pinwheeling is a good indicator of this type of instability.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 2nd, 2020 4:00PM
