Avalanche Forecast
Issued: Dec 20th, 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
Wicked winds have returned! Northwest winds may form wind slabs in areas that are usually more windward, which could catch riders off guard.
Seek out sheltered terrain where you can avoid these wind slabs and better riding.
Summary
Confidence
Weather Forecast
Monday Overnight: Winds increasing overnight, strong from the northwest at ridgetop. Partially cloudy with the chance of very light flurries, trace accumulation. Alpine temperatures around -15 C.
Tuesday: A mix of sun and cloud. Strong to extreme west winds, increasing in the afternoon. Temperatures rising to -8 C in the alpine. Snowfall beginning over night with trace to 5cm of accumulation.
Wednesday: A stormy day. Strong to extreme southwest winds rage on with 5-15 cm of new snow accumulation. Freezing levels rising to around 1000m. Continued snowfall overnight with another 5-15 cm of accumulation.
Thursday: Snowfall continuing into the morning, 5-15 cm of accumulation. Easing into the afternoon with winds backing off moderate to strong southwest at ridgetop. Freezing levels dropping to valley bottom with possible clearing in the afternoon.
Avalanche Summary
On Monday, operators reported one size 2.5 persistent slab avalanche triggered with explosives on a south east aspect at treeline. They also ski cut isolated pockets of wind slab up to size 1.
On Sunday, operators reported isolated size 1 wind slabs with explosive control. They reported whoomphing in previously unskied/uncontrolled terrain.
Snowpack Summary
Saturday's 10-30cm of storm snow will continue to be redistributed by west winds throughout the day. In exposed areas, strong to extreme winds will strip many areas back down to the early December curst and create deposits of hard wind slab in lees. This wind loading may be lower down on slopes than you may expect as a result of the high wind values.
Below this new snow, 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.
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 80-150 cm at treeline elevations and taper quickly below 1900m.
Terrain and Travel
- Be careful as you transition into wind affected terrain.
- 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 storm brought 10-30 cm of new snow. Overnight northwest winds will continue to redistribute this new snow into wind slabs in the alpine and treeline. The northerly component to winds may create loading in areas that are not commonly loaded. In exposed areas, strong to extreme winds will strip many areas back down to the early December curst and create deposits of hard wind slab in lees. This wind loading may be lower down on slopes than you may expect as a result of the high wind values.
Aspects: North, North East, East, South East, South.
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 thick to thin snowpack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 21st, 2021 4:00PM
