Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Sunshine, West Side 93N.
Freezing levels will rise on Sunday, with 5-10 cm of new snow and strong SW winds expected Sunday night and into Monday. Hazard will increase later on Sunday and into Monday as the storm arrives with increased potential for triggering the deep persistent weak layers.
Confidence
Moderate
Avalanche Summary
The recent avalanche cycle produced large natural avalanches in most of the forecast area, with lots of failures on storm snow interfaces and many step downs to the various deeper persistent weak layers in the snowpack. Natural avalanche activity has slowed in the last two days but we are still able to trigger large avalanches with explosives.
Snowpack Summary
Recent storm snow has settled to 20-30 cm above 2300 m. The storm snow sits over buried sun crusts that are present to ridge crests, and faceted layers on shady aspects. Multiple buried crusts are present in the top 50-70 cm on solar aspects. The basal depth hoar is present at the bottom of the snowpack and remains facetted and weak. Low elevations have a temperature crust on all aspects.
Weather Summary
On Sunday, winds will gradually increase into the moderate to strong range out of the SW. Freezing levels will start to rise, reaching 2100-2300 m late in the day. Precip will start in the late afternoon with 5-10 cm expected overnight and into Monday and rain is possible at valley bottom elevations.
Terrain and Travel Advice
- Keep in mind that human triggering potential persists as natural avalanching tapers off.
- If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
- Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
Avalanche Problems
Deep Persistent Slabs
The basal facets, as well as mid-pack facets and crusts, remain a significant concern. Many large avalanches in the recent cycle initiated on or stepped down to these layers, demonstrating that the problem remains widespread and possible to trigger.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 2 - 3.5
Storm Slabs
20-30 of storm snow has formed slabs over previous crusts and facets. While the storm snow has started to bond, it may still be possible to trigger a slab at this interface in steep terrain especially with increasing temperatures or solar heating.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 2.5
Loose Wet
Freezing levels will rise on Sunday, and while solar inputs may be limited, there is still potential for small wet loose avalanches, especially if we get rain at lower elevations later in the day.
Aspects: South East, South, South West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 2