Avalanche Forecast
Purcells
A weak layer is buried at a depth prime to human triggering. As the overlying snow gains slab properties from new snow and warming, destructive avalanches may result. Cautious route finding is advised.
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 at treeline where buried surface hoar may be preserved.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Certain areas in the region have received up to 15 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, as the snow has been falling with southwesterly winds.
Travel and Terrain Advice
- Avoid exposure to terrain traps where the consequence of a small avalanche could be serious.
- Use caution when entering lee areas. Recent wind loading may have created wind slabs.
Avalanche Summary
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
New snow (2-15 cm across the region) has accumulated on surface hoar in sheltered slopes and a sun crust on steep solar aspects. This new snow may be deeper in northwesterly lee features due to moderate southwesterly winds at treeline and alpine elevations.
A warming trend and new snow could create a dangerous slab above buried weak layers in some areas. Numerous persistent weak layers exist in the snowpack. Dry snow overlies two layers composed 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 2400 m. As the overlying dry snow becomes more cohesive and forms a slab, this layer has the potential to create easily-triggerable destructive slab avalanches. Where and when this will occur is tricky to predict and even professionals are scratching their heads about it. It is a good time for conservative decision-making.
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
MONDAY: Cloudy with light snowfall, accumulation 2-5 cm, moderate to strong southwesterly winds, alpine temperature near -5 C, freezing level near 800 m.
TUESDAY: Cloudy with light snowfall, accumulation 5-10 cm, light to moderate southwesterly winds, alpine temperature near -7 C, freezing level near valley bottom.
WEDNESDAY: Partly cloudy with intermittent flurries, light to moderate southwesterly winds, alpine temperature near -14 C, freezing level below valley bottom.
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Around 40 to 80 cm of snow sits above a touchy weak layer. As this snow settles and gains slab properties, a dangerous slab that is easily triggered will likely form.