Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Little Yoho, Sunshine, West Side 93N.
Dangerous avalanche conditions persist with continued evidence every day - on Thursday it was more avalanche control results where "every shot we got a slab" plus observations of large natural avalanches with long fracture propagations in the last 36 hours.
Confidence
High
Avalanche Summary
Observations of natural and explosive-triggered avalanches continued today during an avalanche control mission to the Icefields Parkway. In addition to recent naturals (last 36 hrs), every shot placement resulted in an avalanche, some up to size 3. Most are failing on a mid or lower snowpack persistent weak layer, with long propagations up to 600 m noted in the Cirque Peak area.
Snowpack Summary
Slab avalanches up to 60 cm deep were formed from last week's storm and extreme winds. These slabs overlie several persistent weak layers in the upper snowpack: crusts, facets and surface hoar formed and buried in January and are producing sudden test results. Deeper in the snowpack, the November crust/facet layer 40 cm above the ground also continues to produce sudden test results.
Weather Summary
A ridge of high pressure with a NW flow will keep the region mostly clear and cool until Thursday afternoon when clouds and flurries will begin. Expect the winds to come up on Thursday with the approach of the next system and potentially 5 cm by Friday.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Make conservative terrain choices and avoid overhead hazard.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Avalanche Problems
Persistent Slabs
Slabs 50-100 cm deep overlie three persistent weak layers formed in January (4th, 11th and 22nd) which are a mix of crusts (solar aspect), facets (cold aspects) and isolated surface hoar. Regardless of grain type, snowpack tests consistently show sudden shears on these layers and avalanches are occurring now.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Very Likely
Expected Size: 2 - 3
Deep Persistent Slabs
This problem is at the base of the snowpack and consists of weak facets and depth hoar near an old crust formed in November. The layer is very weak and will not get stronger anytime soon. Thus the upper snowpack sits on an unstable foundation. This problem exists in most locations and requires avoidance or very careful travel through avalanche terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 2 - 3.5
Wind Slabs
Strong winds over the past week have created windslabs and wind-affected snow surfaces in many exposed areas at treeline and above. Use caution in all leeward areas with wind effect. These avalanches have the potential to start small, but then step down to the deeper weak layers.
Aspects: North, North East, East, South East, South.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2