Avalanche Forecast
Issued: Dec 8th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Persistent Slabs and Deep Persistent Slabs.
wlewis,
Avalanche Canada
Watch wind loaded ridge crests and cross-loaded features as recent storm snow gains strength.
As hazard improves, keep in mind that deeper weak layers are still possible to trigger. Steer clear of rocky start zones, where weak layers are shallow.
Summary
Confidence
Weather Forecast
Snowfall tapers as the front exits today, replaced by scattered flurries and mixed cloud until a juicer system approaches this weekend.
WEDNESDAY NIGHT: Flurries continue with moderate west-southwest winds. 2-5cm of snowfall is expected overnight. Freezing levels drop to valley bottom.
THURSDAY: Cloudy with a chance of flurries, moderate westerlies. Freezing levels at valley bottom. Alpine highs of -9.
FRIDAY: Trace amounts of snow, most cloudy. Freezing level at valley bottom, alpine highs of -9. Light westerlies.
SATURDAY: Light to moderate snowfall starts early Saturday morning. Freezing levels climb to 1500m. Alpine highs of -3. Strong to extreme southwest winds.
Avalanche Summary
Explosive control work near Golden yesterday produced several wind slabs up to size 1.5 in steep and unsupported terrain features.
A MIN report submitted on Sunday Dec 5 from the Brewer Creek area reported a column test failure on the Nov 21 SH down 60cm. Several avalanches that occurred in the Toby Creek drainage are thought to have failed on the same layer. This is believed to be lurking around the Toby Creek area, however data is sparse this early in the season and this layer is believed to extend to other areas.
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.
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.
Snowpack Summary
Up to 40cm of storm snow sits over a thick and supportive melt freeze crust on all aspects up to 2400m. Westerly winds have redistributed new snow into deeper deposits in wind loaded features at higher elevations.
A surface hoar layer extends throughout the Toby Creek drainage and surrounding areas - down 30 to 70 cm in sheltered features at treeline and below. Recent snowpack tests have shown this layer to produce sudden propagating fractures. We have limited knowledge of the distribution of this layer, but suspect is its most prevalent between 1900-2400m.
A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. This layer has been reactive to human and explosive triggers, producing large avalanches. This layer is widespread throughout the region 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.
Terrain and Travel
- Be aware of highly variable recent wind loading patterns.
- Avoid slopes that sound hollow or drum-like.
- Avoid areas with a thin or variable snowpack.
Problems
Wind Slabs
Westerly winds and fresh snow continue to build wind slabs in the alpine and treeline. Approach ridge crest and wind loaded features with caution, variable wind directions may create reverse loading patterns. Slabs will be most reactive if they sit on a smooth crust.
Aspects: North, North East, East, South East, South, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A reactive surface hoar layer exists 30-70cm deep in the Toby Creek drainage and surrounding areas. This interface may result in large avalanches with wide propagation and slabs that are more sensitive to human triggers.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
A weak and reactive layer of facets and depth hoar exists at the base of the snowpack above 1900m. While this layer sits deep in the snowpack it has the potential of producing large and destructive avalanches.
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 9th, 2021 4:00PM
