Avalanche Forecast
Issued: Dec 18th, 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
Strong winds will likely have created hard wind slabs in the alpine and treeline. Seek out sheltered terrain where you can avoid wind slabs, find softer snow and enjoy better riding.
Summary
Confidence
Moderate - Uncertainty is due to the extreme variability of wind effect on the snowpack.
Weather Forecast
Saturday Overnight: Extreme southwest winds will ease to moderate overnight and shift to the west. 5-15 cm of new snow can be expected with alpine temperatures dropping to around -12 C.
Sunday: Partially cloudy with light flurries, trace to 3 cm accumulation. Light to moderate ridgetop winds from the west. Alpine temperatures around -10 C, lowering into the evening.
Monday: Mainly cloudy with flurries. Strengthening westerly winds at ridgetop, strong by the afternoon. Alpine temperatures around -12 C.
Tuesday: Partially cloudy with strong to extreme southwest winds. Light flurries, trace accumulation. Alpine temperatures rising throughout the day to around -6 C.
Avalanche Summary
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.
Earlier in the week, operators have reported several large (size 2) explosive-triggered avalanche releasing on the early December crust layer.Â
Snowpack Summary
Yesterday and overnight the region received 10-20 cm of new snow. Strong to extreme southwest will have redistributed this new snow into wind slabs in the alpine and treeline.Â
Below this new snow, more consolidated snow from the previous weekend storm sits over a substantial crust that formed in early December. This crust is likely 20 cm thick (or more) and is present across aspects below 2400m. A thin layer of weak facets (sugary snow) can found above this crust that has demonstrated reactivity in snowpack tests and avalanche activity.Â
Snowpack depths vary due to strong to extreme southwest winds from early December that stripped snow off of exposed areas and deposited it onto lee slopes. Below 2300m, several early season crusts are breaking down and forming a cohesive lower snowpack. Snowpack depths range from 60-110 cm at treeline elevations and taper quickly below 1900m.
Terrain and Travel
- Avoid freshly wind loaded terrain features.
- Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
Problems
Wind Slabs
Yesterday's strong to extreme southwest winds will have redistributed the new snow into wind slabs in the alpine and treeline. Expect loading to be lower down in features than you might usually expect from the high wind values.
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 recently produced large avalanches from explosive triggers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 19th, 2021 4:00PM
