Avalanche Forecast
Purcells
The upper snowpack is starting to consolidate and have slab properties. This snow sits above a buried weak layer at a depth prime to human triggering. Cautious route finding is advised.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Avoid open slopes and convex rolls where buried surface hoar may be preserved.
- Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.
- Use conservative route selection. Choose moderate-angled and well-supported terrain.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Certain areas in the region have received up to 20 cm of snow, which sits on a variety of surfaces that the new snow may not bond well to. Snow depths may be higher in northeasterly lee features.
Travel and Terrain Advice
- Use caution when entering lee areas. Recent wind loading may have created wind slabs.
- Avoid exposure to terrain traps where the consequence of a small avalanche could be serious.
Avalanche Summary
A slab avalanche was noted in a lee feature in alpine terrain within the recent storm snow, about 15 cm deep.
Numerous signs of instability have been noted in the snowpack over the past week, including whumpfing and cracking between 1700 and 2100 m, and two skier-triggered avalanches suspected to have released on the December 15 weak layer. Expect the potential to trigger persistent slabs to increase as the snow continues to settle into a cohesive slab.
Please share your recent observations through the Mountain Information Network.
Snowpack Summary
10-20 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, this new snow is 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. Dry snow overlies layers of weak and feathery surface hoar, with the deeper layer (December 15) buried 40 to 80 cm. This layer is found most often around and below treeline but has been reported as high as 2450 m and could exist higher. As the overlying dry snow becomes more cohesive and forms 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
TUESDAY: Cloudy with light snowfall, accumulation 5-15 cm, light to moderate westerly winds, alpine temperature near -8 C, freezing level near 1200 m.
WEDNESDAY: Partly cloudy with intermittent flurries, light to moderate westerly winds, alpine temperature near -14 C, freezing level below valley bottom.
THURSDAY: Cloudy with snowfall, accumulation 5-10 cm, moderate southwesterly winds, alpine temperature near -10 C, freezing level below valley bottom.
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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.