Avalanche Forecast
Purcells
A weak layer is buried at a depth prime to human triggering. As the overlying snow settles and forms a slab, destructive avalanches will likely result. Cautious route finding is advised, particularly at treeline elevations.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Avoid open slopes and convex rolls at treeline 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 Summary
Several small loose wet avalanches were observed on steep solar faces and gullies on Wednesday.
Whumpfing and cracking was observed in the north of the region on Tuesday between 1700 and 2100 m.
Last weekend, a size 1.5 avalanche involving two people near Invermere was reported. It was suspected to have run on the mid-December weak layer. Also, a skier triggered a size 2 persistent slab avalanche running on a layer of facetted snow from mid-December. This happened in the north of the region's Dogtooth Range on a west aspect at 2400m.
Expect the potential to trigger persistent slabs to increase as last week's storm snow continues to settle into a cohesive slab.
Snowpack Summary
A warming trend is creating 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.
The snow surface is variable, consisting of dry snow on shaded aspects, a sun crust on steep solar aspects, and wind effect in exposed alpine and treeline locations.
Deeper in the snowpack at depths of about 70 to 110 cm, a rain crust from November is producing variable snowpack test results, from sudden fracture characters to no result. This layer is considered dormant for now, but could be triggered where the snowpack is thin.
Please share your recent observations through the Mountain Information Network.
Weather Forecast
FRIDAY: Mostly cloudy, light southwesterly winds, freezing level near valley bottom.
SATURDAY: Cloudy with light snowfall, accumulation 2-5 cm, light southwesterly winds, freezing level near valley bottom.
SUNDAY: Cloudy with light snowfall, accumulation 1-3 cm, light southwesterly winds, freezing level near valley bottom.
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Around 40 to 80 cm of snow sits above a touchy weak layer. As this snow settles and becomes more cohesive, a dangerous slab that is easily triggered will likely form.