Avalanche Forecast
Purcells
Rapid snowfall loading is expected for parts of the region. New snow and buried layers will likely be reactive to natural and human triggers, producing destructive avalanches that could run full-path. Best to avoid avalanche terrain.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- A good day to avoid avalanche terrain, giving wide berth to overhead exposure.
- Choose shallow-angled and sheltered terrain where new snow hasn't been wind-affected.
- If triggered, the storm/wind slabs may step down to deeper layers, resulting in large avalanches.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Several weak layers are lurking in our snowpack, which are producing very large avalanches that propagate far, with high consequences. Snowfall is rapidly loading these layers, increasing the likelihood of triggering them. These could run full-path.
Travel and Terrain Advice
- Make conservative terrain choices and watch for clues of instability.
- Be aware of the potential for wide propagation.
- Avoid open slopes and convex rolls where buried surface hoar may be preserved.
Avalanche Summary
Many small to large (size 1.0 to 2.5) slab avalanches were observed on Tuesday, including storm, wind and persistent slabs. The storm/wind slabs were 10 to 40 cm deep, on all aspects, all elevation bands, and triggered by skiers and explosives. The persistent slabs released on the early-January layer described in the section below, were triggered by explosives, and were generally 100 to 120 cm deep. Similar avalanches were reported between Friday and Monday, showing a steady trend of avalanche activity.
Looking forward, dangerous snowpack conditions will persist in the region on Thursday with new snowfall. This trend will likely continue until a more stable weather pattern governs and we see a decrease in avalanche observations. All of our buried weak layers continue to produce large, destructive avalanches from natural and human triggers. Recent storm and wind slabs have the potential to step down to deeper weak layers, which could produce very large avalanches with high consequences.
Snowpack Summary
Between 30 and 70 cm of snow could accumulate with this storm by Thursday afternoon, with the most in the southwest of the region. This new snow overlies preexisting storm and wind slabs. All of this overlies a complex and generally weak snowpack structure with four active weak layers that we are monitoring:
1) 70 to 110 cm of snow overlies a crust and/or surface hoar layer from mid-January. The crust is reportedly widespread, except for possibly high elevation north aspects. The surface hoar is 10 to 30 mm in size and exists at all elevation bands.
2) The early-January persistent weak layer is 80 to 130 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is found at all elevation bands. Recent snowpack tests have shown sudden fracture characters with moderate loads and high propagation potential.
3) Another weak layer buried mid-December consists of a facet/surface hoar/crust combination, which is buried 100 to 150 cm deep. It is most problematic at and below tree line.
4) A crust/facet layer from late November is yet another weak layer, which has recently produced very large, destructive avalanches.
Weather Forecast
THURSDAY: Cloudy with snowfall, accumulation 10 to 25 cm in the north of the region and up to 40 cm in the southwest of the region, moderate westerly winds, alpine temperature -6 C dropping to -15 C, freezing level near 1500 m in the south of the region and dropping to below valley bottom.
FRIDAY: Partly cloudy with possible valley cloud, light to moderate northerly winds, alpine temperature near -14 C, freezing level below valley bottom.
SATURDAY: Mostly sunny, light to moderate westerly winds, alpine temperature near -12 C, freezing level below valley bottom.
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Between 30 and 70 cm of snow may accumulate with this storm, with the highest amounts in the southwest of the region. This snow may be reactive to triggering, and if so, could step down to buried weak layers. Expect deeper snow in lee features.