Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Sunshine, West Side 93N.
Start and finish early. Solar radiation will increase the likelihood of all of the described avalanche problems as the day progresses on Monday.
Human triggering of the persistent weak layers is much more of a concern in these shallow snowpack areas compared to areas to the West that are described in the Little Yoho bulletin.
Confidence
Moderate
Avalanche Summary
No new avalanches were observed at the time of writing Sunday.
On Saturday, skiers in the Ferris Glacier area remote-triggered a wind slab 60 cm deep on NE alpine terrain.
On Friday, skiers remote triggered a wind slab, possibly over a recent crust, on St. Nicholas size 2.5 that stepped down to deeper layers and occurred on steep, unsupported terrain.
Snowpack Summary
10-20 cm of dry snow overlays crusts found in most locations, with up to 60 cm on north-facing alpine zones. Windslabs can be found on lee aspects in the alpine.
The lower half of the snowpack is facets and depth hoar beneath a 30-60 cm stiff midpack slab. On all but high north aspects, upper snowpack crusts overlay this midpack slab. If these crusts are thick and remain frozen, they provide some strength over the weakness. On high north slopes, this weakness remains a concern.
Weather Summary
Clearing overnight Sunday with treeline temperatures dropping to -10°C while W/NW winds diminish to light.
Monday, a mix of sun and cloud as the freezing levels rise to 2400 m. Significant solar effects are likely. West winds increase to moderate. Overnight temperatures at treeline will drop to -7°C.
Terrain and Travel Advice
- Watch for newly formed and reactive wind slabs as you transition into wind-affected terrain.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Avalanche Problems
Wind Slabs
Strong SW-NW winds Thursday, Friday and moderate winds Saturday combined with recent snow built slabs in lee features and contributed to fresh cornice development. Last night's 10-15 cm of snow will now bury these. On solar slopes thinner slabs may be touchy as they overlie more recent sun crusts.
Aspects: All aspects.
Elevations: Alpine.
Likelihood: Likely
Expected Size: 1 - 2
Loose Wet
With more sun expected Monday and freezing levels expected to rise, expect recent snow to slide over buried crusts on steep solar slopes. At lower elevations, surface crusts may start to break down leading to difficult travel and increasing hazard.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 2
Persistent Slabs
A midpack slab up to 80 cm thick sits on the weak, facetted lower snowpack. On all but high north aspects, recent sun crusts and the March 27 rain crust cap this slab, providing some security. Use caution in higher, thin snowpack areas or where these crusts are weak or breaking down with heating.
Aspects: North, North East, East, West, North West.
Elevations: Alpine.
Likelihood: Possible - Likely
Expected Size: 2 - 3