Avalanche Forecast
Purcells
Slab formation over our buried weak layers has been gradual, but it's now a reality. Avalanche activity is increasing and current conditions demand low angle, low consequence terrain selection.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Use conservative route selection. Choose moderate-angled and well-supported terrain.
- Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.
- Avoid open slopes and convex rolls where buried surface hoar may be preserved.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
20-30cm of recent snow is sitting on a range of variable surfaces and it will need more time to form a solid bond to them. The new snow is likely to be particularly reactive where it has been affected by the wind.
Travel and Terrain Advice
- Avoid exposure to terrain traps where the consequence of a small avalanche could be serious.
- Use extra caution in wind affected areas. Recent wind loading has created wind slabs.
Avalanche Summary
Reports from Monday included observations of several wind slab, storm slab, and persistent slab releases from Size 1-2. Several storm slabs released naturally, while others were triggered by skier traffic or explosives testing. Most activity was focused on northwest to northeast aspects, however wind slabs were observed on all aspects. Slab depths ranged from 20-70 cm, owing to both wind effect as well as the variety of failure planes currently active.
Numerous signs of instability have been noted in the snowpack over the past week, including whumpfing and cracking between 1700 and 2100 m, as well as two skier-triggered avalanches suspected to have released on the December 15 weak layer. Expect the potential to trigger persistent slabs to remain heightened as the upper snowpack continues to settle into a cohesive slab.
Please share your recent observations through the Mountain Information Network.
Snowpack Summary
15-25 cm of new snow is forming a storm slab and sitting on surface hoar in sheltered slopes and a sun crust on steep solar aspects. The snow fell with moderate to strong southwesterly winds in the alpine, which produced wind slabs in lee features at treeline and alpine elevations. Below treeline, storm slabs are mainly a concern in openings (e.g. cut blocks, gullies, cut banks).
A warming trend and new snow is likely creating a dangerous slab above buried weak layers. About 40-80 cm of snow now overlies a layer of weak and feathery surface hoar from December 15. This layer is found most often around and below treeline but has been reported in the alpine as well. As the overlying snow continues to consolidate into a slab, this layer has the potential to create easily-triggerable, destructive slab avalanches. This has occurred in neighbouring forecasting regions with a similar snowpack.
Deeper in the snowpack (70 to 110 cm), a November crust is producing variable snowpack test results, from sudden fracture characters to no result. This layer is considered dormant but could be triggered where the snowpack is thin.
Weather Forecast
Wednesday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds. Alpine high temperatures to around -8.
Thursday: Mainly cloudy with isolated flurries and a trace to 5 cm of new snow. Light variable winds. Alpine high temperatures to around -7.
Friday: A mix of sun and cloud. Moderate west winds. Alpine high temperatures to about -7.
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Around 40 to 80 cm of snow sits above a touchy weak layer. Recent reports indicate that this snow is consolidating and gaining slab properties and could be triggered by humans.