Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Little Yoho, Sunshine, West Side 93N.
The snowpack is becoming increasingly complex.
Incremental inputs of snow with wind and mild temperatures are prompting the development of slab properties in the upper snowpack.
"Arctic Facets" from the cold snap fall apart easily in steep terrain and a layer of surface hoar or sun crust buried early in January lingers in some areas
Confidence
Moderate
Avalanche Summary
Avalanche control Monday on Mt Whymper produced several avalanches to size 2.5 starting at 2700 m and running to the top of the runout zones. These were 20-40 cm wind slabs that ran further than expected in the loose surface snow. Control in the Simpson area produced several size 2 avalanches at 2200m, failing 40 cm down on surface hoar and propagating 50-70 meters wide.
Snowpack Summary
Two weak layers each produce test results in some locations across the region as slab formation is taking place in the upper snowpack. Facets are buried down15cm and a layer of surface hoar sits at about 40cm deep.
The midpack offers some strength and features two crusts that persist as high as 2350m.
The lower part of the snowpack has weak facets and depth hoar and widespread whumphing has been observed in many locations over the last week.
Monday's snow profile from Simpson.
Weather Summary
We should expect flurries throughout the day on Wednesday with strong to extreme winds at higher elevations. Look for temperatures to cool slightly after warmer weather pushed in on Tuesday. Expect freezing levels to return to valley bottom.
Terrain and Travel Advice
- Avoid areas where the snow feels stiff and/or slabby.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Use appropriate sluff management techniques.
Avalanche Problems
Wind Slabs
Warm temps, wind, and fresh snow will continue to promote the development of slab properties in the upper snowpack. Slabs sit on facets down 15 (arctic facets) and surface hoar down 30-40 (Dec 31). Test results and avalanche activity indicate this layer is sensitive and human triggering is likely.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1.5 - 2.5
Loose Dry
Dry facets in the upper snowpack have been producing skier-triggered sluffs earlier this week. Evidence of the same problem was observed in KNP, where older loose, facet avalanches had run far down gullies in steep terrain. A buried crust on steep solar slopes may make this problem more sensitive.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood: Likely
Expected Size: 1 - 1.5
Deep Persistent Slabs
The base of the snowpack consists of weak facets, depth hoar, and the overlying crust in the midpack continues to break down. Use caution in steep terrain, large planar slopes, and thin to thick areas where initiating these slabs would be more likely.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1.5 - 3