Avalanche Forecast
Issued: Dec 19th, 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
Human triggered wind slabs remain likely as strong winds are expected to form fresh slabs throughout the day.
A buried persistent weak layer continues to warrant careful terrain selection and diligent decision making.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Sunday Overnight: Light northerly winds and partially cloudy skies. Temperatures dropping to -16 C in the alpine.Â
Monday: Mainly cloudy with a chance of flurries. Alpine temperatures around -10 C. Strong southwest winds at ridgetop. Â
Tuesday: A mix of sun and cloud. Strong southwest winds at ridgetop, reaching extreme in the afternoon. Temperatures rising with an alpine high of -7 C. Cloud cover increasing into the evening.
Wednesday: Cloudy and snowing, 3-15 cm accumulation. Strong to extreme southwest winds at ridgetop. Alpine temperatures around -8 C.
Avalanche Summary
On Sunday, operators reported isolated size 1 wind slabs with explosive control. They reported whoomphing in previously unskied/uncontrolled terrain.
On Saturday, operators observed cracking, whoomphing, and skier triggered wind slabs up to size 1.
On Friday, the South Rockies field team was out in the Window Mountain area. They observed several natural wind slab avalanches in the alpine up to size 1.5. Read their full report here.
Snowpack Summary
Saturday's 10-20cm of storm snow was redistributed by moderate to strong winds into wind slabs in the alpine and treeline. This new snow overlies a variety of wind effected surfaces formed by strong to extreme winds, stripping many areas in the alpine and exposed treeline and creating hard wind slab in others.
Below this, a layer of more consolidated snow sits over a substantial crust that formed in early December. This crust is up to 20cm thick and is present across all aspects below 2400m. Up to 10cm of faceting has been reported above this crust. This problem is particularly hard to predict and tricky to manage. For this reason wide, conservative terrain margins and disciplined backcountry travel techniques will be very important. Get more details and photos in our forecaster blog.Â
Snowpack depths vary due to strong to extreme southwest winds that stripped snow off of exposed areas and deposited it onto lee slopes. Below 2300m, several early season crusts make up the lower snowpack. Snowpack depths range from 60-100 cm at treeline elevations and taper quickly below 1900m.
Terrain and Travel
- Be careful as you transition into wind affected terrain.
- Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
- Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
- Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
Problems
Wind Slabs
Saturday's 10-30cm of new snow has been redistributed by southwest winds into wind slabs in the alpine and treeline. As the winds pick up today, the new snow that remains loose and unconsolidated will be redistributed into fresh, reactive wind slabs in the alpine and treeline.
Aspects: North, North East, East, South East, South, 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 produced large avalanches from explosive triggers and has shown reactivity in snowpack tests. Avoid likely trigger spots such as steep, convex slopes, with a shallow or thin to thick snowpack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 20th, 2021 4:00PM
