Avalanche Forecast
Issued: Dec 11th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Deep Persistent Slabs.
bchristie,
Avalanche Canada
Continue to choose mellow slopes protected from the wind.
Wind and new snow are building slabs that can be triggered by a rider. It is still uncertain how well this new snow is bonding to the snowpack.
Summary
Confidence
Low - Uncertainty is due to how the snowpack will react to the forecast weather.
Weather Forecast
SATURDAY NIGHT: Mostly cloudy. 5-10cm of snow expected. Moderate southwest winds, possibly extreme on high peaks. Freezing levels between 1000 and 1300m, starting to drop again around midnight.
SUNDAY: Mostly cloudy. 0-7 cm snow expected. Moderate to strong southwest wind. Freezing levels below 1000m. Alpine highs of -6 C.Â
MONDAY: Mostly cloudy. 0-5 cm snow expected. Light to moderate south winds. Warming through the day, alpine high around -7 C.
TUESDAY: Mostly cloudy. Possible trace of snow. Light to moderate SW winds. Alpine high around -8 C.
Avalanche Summary
No new avalanches observed. Expect human triggered avalanches to remain likely as the storm snow settles.
On Wednesday, natural and skier triggered slab avalanches were observed at treeline and above to size 1.5.
Explosive control work near Golden on Dec 5th produced a size 2 slab avalanche that failed to ground in a steep and unsupported terrain feature. A naturally triggered size 3 was also observed on a west facing slope in the Northern zone of the Purcells, believed to have occurred around the 2nd of December.Â
Two Mountain Information Network (MIN) reports (MIN 1 and MIN 2) from Dec 3 in Quartz Creek also reported deep persistent avalanches failing at the base of the snowpack.Â
While these observations are a week old, this deeply buried weak layer is still a concern.
Snowpack Summary
Moderate to strong southwest winds continue to redistribute 20-30cm of recent storm snow, forming reactive slabs.
The new storm snow overlies about 50cm of settling snow from the last storm. This sits on a thick, supportive melt freeze crust on all aspects up to 2400m (December 2nd).Â
Where the December 2nd crust does exist, facets may be forming on top, making this a layer to watch.
A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. This layer has been reactive to human triggers, producing large avalanches. This layer is widespread and will likely continue to be a layer of concern.
Average snowpack depth at treeline is 100-180cm, with the deepest snowpack found near the Bugaboos.Â
Terrain and Travel
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Closely monitor how the new snow is bonding to the crust.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Be mindful that deep instabilities are still present and have produced recent large avalanches.
Problems
Storm Slabs
Underneath the storm snow, there are lingering wind slabs on most aspects, due to recent, strong winds of varying direction. An avalanche that starts in the storm snow has the potential to step down to these wind slabs, that were most prominent at treeline and in the alpine.
If you are unsure where the old wind slabs are lurking, then assume any storm slab avalanche has the potential to get bigger than expected.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
A widespread weak layer of facets and depth hoar exists at the base of the snowpack above 1900m.
Avoid thin and rocky start zones where this layer may sit closer to the surface, and big open slopes capable of producing large avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 12th, 2021 4:00PM
