Avalanche Forecast
Regions: Lizard-Flathead.
The ridgetop winds will be cranking Monday night and 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.
Confidence
Low - Uncertainty is due to limitations in the field data.
Weather Forecast
Tuesday: Mainly cloudy. Light snow amounts possible 5-10 cm. Alpine temperatures near -3 and ridgetop wind strong southwest above 2200 m. Freezing levels 1100 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 1000 m.
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 recent avalanche activity has been reported.
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 but we may see an increase in wind slab avalanche activity with the forecast strong to extreme ridgetop wind on Tueday.
Snowpack Summary
Widespread surface hoar growth (feather-like frost crystals) exists on most aspects and elevations and especially in wind-sheltered areas. Check out these great photos from Coal Creek, Wranglers Cabin, and Harvey Pass. The formation and distribution of the surface hoar will be important to track ahead of the next snowfall. I suspect strong 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 see it transition to our problems page once additional new snow buries it. It is a layer to track and monitor as the season progresses.Â
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.Â
The snowpack is thin and variable in wind-scoured areas, and it tapers rapidly at lower elevations. Snowpack depths at sheltered upper treeline elevations are nearing 100 cm and beginning to exceed the threshold for avalanches.Â
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.
Avalanche 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: Possible
Expected Size: 1 - 2