Avalanche Forecast
Issued: Dec 16th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
zryan,
Avalanche Canada
As the sun comes out today, solar input has the potential to substantially increase the reactivity of a buried persistent weak layer. This will demand conservative terrain travel and diligent decision making. Read more about this problem in our forecaster's blog here.
Summary
Confidence
Weather Forecast
Thursday Overnight: Cloudy with flurries in the evening, 5-10cm of new snow accumulation. Clearing overnight with temperatures plummeting in the -20s in the alpine. Moderate to strong northwest winds at ridgetop.
Friday: Clear skies and cold temperatures. Alpine temperatures between -15C to -20C with chilling moderate to strong northwest winds. Increasing cloud cover and winds in the evening with a low pressure system moving across BC.
Saturday: Mainly cloudy with flurries, 5-10cm of accumulation. Strong to extreme westerly winds at ridgetop with freezing levels rising to 1000m in the afternoon.
Sunday: Winds and snow easing overnight, another 5cm of accumulation in the evening. A partially cloudy day with flurries. Strong southwest winds easing to light in the afternoon.
Avalanche Summary
Over the last two day, operators have reported several large (size 2) explosive-triggered avalanche releasing on the early December crust layer.
Observations from last weekend indicated that the snowpack was quite touchy. Avalanche control with explosives and ski cuts produced several size 2 avalanches, and one size 3. Most failed on top of the rain crust from the late November/early December rain events.
Snowpack Summary
Up to 30 cm of snow has accumulated since Monday. This unconsolidated new snow will be redistributed by northwest winds into fresh, reactive wind slabs in the alpine and treeline.
Below this layer, more consolidated snow from the previous weekend storm sits over a substantial crust that formed in early December. This crust is likely 20 cm thick (or more) and is present across aspects below 2400m. A thin layer of weak facets (sugary snow) can found above this crust that has demonstrated reactivity in snowpack tests and avalanche activity.
Snowpack depths vary due to strong to extreme southwest winds from early December that stripped snow off of exposed areas and deposited it onto lee slopes. Below 2300m, several early season crusts are breaking down and forming a cohesive lower snowpack. Snowpack depths range from 60-110 cm at treeline elevations and taper quickly below 1900m.
Terrain and Travel
- Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
Problems
Wind Slabs
This week's 30cm of new snow will continue to be redistributed by northwest winds into fresh, reactive wind slabs in the alpine and treeline. Yesterday, southwest winds will have created wind slabs in lee features, which will likely be more stubborn to human triggering.
Aspects: North, North East, East, South East, South, South West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A layer of weak facets (sugary snow) can be found down 40-70 cm over a crust that formed in early December. This layer has recently produced large avalanches from explosive triggers. As the sun comes out today, we may see substantial warming which will increase the reactivity of this layer and warrant conservative terrain selection.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 17th, 2021 4:00PM
