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: A cloudy evening with flurries, trace to 5cm of accumulation. Clearing overnight with temperatures plummeting into the -15C to -20C range in the alpine. Light to moderate northwest winds at ridgetop.
Friday: Clear skies and cold temperatures. Alpine temperatures in the -15C to -20C range, a slight temperature inversion is possible in the morning. Light to moderate northwest winds at ridgetop. Cloud cover and winds increasing overnight, trace to 10 cm of new snow accumulation
Saturday: A mainly cloudy day with flurries, trace to 10cm of accumulation. Strong to extreme southwest winds at ridgetop and alpine temperatures around -12 C.
Sunday: Partially cloudy with isolated flurries. Light to moderate westerly winds at ridgetop with alpine temperatures around -13 C.
Avalanche Summary
On Wednesday, avalanche control triggered a very large (size 3) avalanche on a northwest aspect around 2050 m that released on the early December weak layer.
On Tuesday, a large (size 2) avalanche was remotely-triggered on this same layer by a skier. This occurred on a west aspect near 2100 m and broke 100 cm deep.
On Sunday, a small, skier remote triggered avalanche was reported that failed on a reloaded bed surface near the base of the snowpack on a north aspect in the alpine. There were other deep failures reported in this region about a week ago. This information is spotty, but it is consistent with a deep persistent problem that may be difficult to trigger. We're not done worrying about this one yet.
Snowpack Summary
Between 20-40 cm of snow has accumulated this week. Periods of moderate wind from varying directions this week have created wind slabs in the alpine and open treeline . With snow available for transport, be aware of the potential for today's northwest wind to form new reactive wind slabs in lee terrain features.
Below this layer, consolidated snow from the previous weekend storm sits over a substantial crust that formed in early December. This crust is 10-40 cm thick and can be found down 40-80 cm. It is present across aspects below 2300m. A thin layer of weak facets (sugary snow) can found above this crust that has demonstrated reactivity in snowpack tests and recent avalanche activity.
A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. Although this layer has been trending less reactive, it remains on our radar.
The snowpack depth at treeline is around 115-200 cm. The deepest snowpack can be found near the Bugaboos.
Terrain and Travel
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- In times of uncertainty conservative terrain choices are our best defense.
Problems
Wind Slabs
Be alert to changing conditions. Winds are forecast to shift to the northwest and increase at upper elevations, which may form fresh wind slabs that are reactive to human triggering. Previous moderate to strong southwest to southeast winds built slabs in leeward terrain and may also remain possible to trigger.
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. As the sun comes out today, recent snow is settling and stiffening above and this layer, it may beginning to produce avalanches and definitely warrants conservative terrain selection.
At the base of the snowpack above 2200 m, a layer of depth hoar lingers. Avalanches-in-motion have the potential to step down to this layer.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 17th, 2021 4:00PM
