Avalanche Forecast
Issued: Dec 7th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
swerner,
Avalanche Canada
The ridgetop winds are cranking Monday night into Tuesday. Heads up! There may be fresh and reactive wind slab in the alpine and "alpine-like" terrain features. Stiff snow that's cracking beneath your feet are good indicators of wind slab.
Summary
Confidence
Weather Forecast
Tuesday: Mix of sun and cloud. Alpine temperatures near -1 and ridgetop wind strong to extreme above 2200 m. Freezing levels 1200 m.
Wednesday: Mostly cloudy with some sunny periods. Light snow 5-10 cm possible. Alpine temperatures near -5 and ridgetop wind light to moderate gusts from the southerly quadrants. Freezing levels at valley bottom.
Thursday: Mix of sun and cloud. Alpine temperatures near -10 with freezing levels at valley bottom. Ridgetop winds light from the southwest
Avalanche Summary
No new avalanches were reported on Monday.
At the beginning of last week's strong temperature inversion, small (up to size 1.5) loose wet avalanches were observed on steep solar slopes and in extreme rocky terrain.
There have been no reports of large avalanches in the past week. The most recent wind slab avalanche activity was reported at the end of November.
Snowpack Summary
Widespread surface hoar growth (feather-like frost crystals) exists on most aspects and elevations and especially predominant win wind-sheltered areas. Check out these great photos (here, here, and here) from our close neighbors in the Lizard/Flathead region. The formation and distribution of the surface hoar will be important to track ahead of the next snowfall. I suspect strong to extreme alpine wind forecast on Tuesday may rid this crystal from wind-exposed slopes and terrain. Isolated pockets of stiff and reactive wind slab may exist on leeward slopes during and after this wind event. These wind slabs may sit above a widespread rain crust from early November, which can be found up to 2500m and buried down 30-100cm. Weak snow may be developing around this crust.
However, given the stagnant weather pattern and a decreasing trend in instability, this problematic snowpack structure is not currently listed as a problem. We may expect to see it transition to our problems page once it becomes buried with new snow. It will be a layer to monitor as the season progresses.
After several days of clear skies and warm air in the alpine, temperatures are returning to their seasonal normal, and melt-freeze crusts have been left behind on solar aspects.
The snowpack is thin and variable in wind-scoured areas and tapers rapidly at lower elevations. Snowpack depths at sheltered upper treeline elevations are nearing 100 cm and beginning to exceed the threshold for avalanches.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Small avalanches can have serious consequences in extreme terrain. Carefully evaluate your line for wind slab hazard before you commit to it.
- Watch for areas of hard wind slab on alpine features.
Problems
Wind Slabs
Strong to extreme wind forecast for overnight Monday and into Tuesday may create new and reactive wind slabs on lee and cross-loaded features in the alpine and in "alpine-like" features near treeline, particularly where these slabs sit on top of a crust/facet layer from early November.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 8th, 2020 4:00PM
