Avalanche Forecast
Regions: South Rockies.
Fresh wind slabs will likely form in new places as winds change direction and increase. Stick to sheltered areas and be mindful of overhead hazards on Friday.
Confidence
Moderate - Forecast snowfall amounts are uncertain.
Weather Forecast
Thursday night: Cloudy, up to 5 cm of snow, moderate northeast winds, alpine temperature -12 C.
Friday: Cloudy, 5-10 cm of snow, strong northeast winds, alpine high temperature -15 C.
Saturday: Cloudy, 5-15 cm of snow, strong northeast winds, alpine high temperature -20 C.
Sunday: Mix of sun and cloud, light northeast winds, alpine high temperature -10 C.Â
Avalanche Summary
Strong winds are expected to form fresh wind slabs that may be reactive to human triggers. Cornices have also grown large with the recent weather, and a cornice failure could trigger a wind slab avalanche on the slope below.Â
There have been recent reports of large (size 2-2.5) explosive-triggered avalanches releasing 20-30 cm deep in the storm snow. In a few cases in the neighbouring Lizard Range and Flathead region, these avalanches were triggered by cornice falls.
Snowpack Summary
Up to 15 cm of new snow may accumulate by Friday afternoon. Winds are forecast to shift to the northeast and to increase to 40-60 km/hr, building fresh wind slabs in a reverse-loading pattern.
A total of 25 to 45 cm of snow from the previous storm has been redistributed by wind or is well-settled. This snow sits on older wind slabs in exposed areas, and a sun crust on solar aspects (south through west facing slopes). Melt-freeze crusts extend up to about 1900 m on other aspects.Â
A thick crust/facet layer currently sits 40-80 cm below the surface and can be found up to 2100 m. The middle of the snowpack is generally strong, but the base of the snowpack contains basal facets that are most prominent in shallow rocky start zones.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Avoid exposure to slopes that have cornices overhead.
- Be aware of the potential for large avalanches due to the presence of a deep persistent slab.
Avalanche Problems
Wind Slabs
Winds are forecast to change direction to the northeast and increase. There is ample snow for transport with this reverse-loading pattern, and another 15 cm of new snow is possible by Friday afternoon. These winds are expected to drift recent snow into fresh wind slabs that may be reactive to human triggering. Given recent variability in wind direction, few aspects will be spared from wind slab concerns.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible - Likely
Expected Size: 1 - 2
Deep Persistent Slabs
Weak snow at the bottom of the snowpack hasn't gone away. Evidence of deep persistent slab avalanches has been focused in the Sparwood-Elkford area over the past month. Human triggering is most likely around steep rocky terrain features, or anywhere the snowpack is thin and weak. Cornices have grown large and loom over many ridge lines, a failing cornice could initiate a deep persistent slab when it impacts the slope below.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Unlikely - Possible
Expected Size: 2.5 - 3.5