Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Little Yoho, Sunshine, West Side 93N.
Avalanche activity up to size 2.5 continues to be observed - if you're watching the MIN, you can see the hazard building: a bit more triggering each day, two weak layers in the upper snowpack producing test results, and slightly larger avalanches each day. This is a snow and steady pattern of incrementally building avalanche hazard.
Confidence
Low
Avalanche Summary
Avalanche control today 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 windslabs 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
The upper 30-50 cm of the snowpack is tricky. Two weak layers buried down about 15 and 40 cm produce test results across the region as the overlying slab is failing and propagating. This slab will continue to develop with Tuesday's wind and warming, and human triggering is expected. The lower part of the snowpack has weak facets and depth hoar and widespread whumphing has been observed in many locations.
Monday's snow profile from Simpson.
Weather Summary
What a change from a week ago, as the storm track now crosses our area bringing light snow, warming temperatures and strong winds. Typical Chinook pattern where the eastern side of the park will be windy (extreme winds on Tuesday) and snow/rain to the west. Expect up to 5 cm over the day on Tuesday with valley bottom temperatures reaching +3 and freezing levels up to 1800 m.
Terrain and Travel Advice
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Avalanche Problems
Wind Slabs
Windslabs exist and will continue to build on Tues. These 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. Choose smooth planar terrain and avoid drifted areas.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1.5 - 2.5
Loose Dry
Dry facets exist in the upper snowpack and have been shown to produce skier-triggered sluffs below the treeline earlier this week. Evidence of the same problem was observed at treeline near Simpson, where older loose, facet avalanches had run far down gullies.
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 continues to break down. Use caution in steep terrain, areas with wind slabs (step-down potential), large planar slopes, and thin to thick areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1.5 - 3