Avalanche Forecast
Purcells
More snowfall will continue to load storm and wind slabs as well as several buried persistent weak layers. All of these will likely be reactive to natural and human triggers. Be disciplined: perform cautious route-finding and avoid overhead exposure.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Use ridges or ribs to avoid pockets of wind-loaded snow.
- Seek out 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 continue to produce very large avalanches with high consequences. Limit your exposure to avalanche terrain and avoid overhead hazards.
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 very large (size 1.0 to 3.5) slab avalanches were observed on Monday, including storm/wind slabs and persistent slabs. The storm/wind slabs were 30 to 70 cm deep, on all aspects, all elevation bands, and triggered naturally and by heavy loads. The persistent slabs released on all of the layers described in the section below, were triggered naturally, by skiers, and explosives, at all elevation bands, and were generally 100 to 150 cm deep. Similar avalanches were reported between Friday and Sunday, showing a steady trend of avalanche activity.
Looking forward, dangerous snowpack conditions will persist in the region, particularly with forecasted snowfall on Wednesday. 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 (described below) continue to produce large, destructive avalanches from natural and human triggers. Recent storm slabs and wind slabs have the potential to step down to deeper weak layers, which could produce large, destructive avalanches.
Snowpack Summary
Up to 20 cm of snow could accumulate in the region on Wednesday. This overlies storm and wind slabs from previous storms with strong winds. These storm and wind slabs overly 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
WEDNESDAY: Cloudy with snowfall, accumulation 5 to 20 cm with the most in the southwest of the region, moderate westerly winds, alpine temperature near -6 C, freezing level near 1500 m in the south of the region.
THURSDAY: Cloudy with snowfall, accumulation 10 to 20 cm, moderate westerly winds, alpine temperature near -10 C, freezing level below valley bottom.
FRIDAY: Partly cloudy with possible valley cloud, light to moderate northwesterly winds, alpine temperature near -15 C, freezing level below valley bottom.
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New snow on Wednesday as well as previously formed storm and wind slabs will likely be reactive to both natural and human triggering. If triggered, avalanches could step down to deeper weak layers.