Avalanche Forecast
Regions: Sea To Sky.
Wind slabs may be found on a variety of aspects and will likely remain sensitive to human triggers Friday.
A persistent weak layer is now buried up to 100 cm. Avalanches on this layer will become harder to predict, so maintaining a conservative approach is key.
Confidence
Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.
Weather Forecast
Thursday night: Flurries, trace to 5 cm new snow, strong northwest ridgetop wind, alpine temperature near -6.
Friday: Mix of sun and cloud, strong northwest wind easing to light, alpine high -5, freezing level 1000 m.
Saturday: Mainly cloudy, moderate westerly wind, alpine high temperature -7, freezing level 900 m.
Sunday: Mix of sun and cloud, light westerly wind, alpine high temperature -10, freezing level valley bottom.
Avalanche Summary
In the clear weather on Wednesday, evidence of a widespread natural storm slab avalanche cycle was observed. It is suspected to have occurred during the storm on Monday night.
There have been reports of numerous size 1-2 natural, human and explosives triggered avalanches every day since Saturday. Many of these avalanches have failed on the recently buried persistent weak layer. Most recently, explosive control work conducted on Wednesday produced size 2 cornice and storm slab avalanches.
Snowpack Summary
50-100 cm of recent snow sits on a persistent weak layer that consists of facets at upper elevations, surface hoar in sheltered areas, a melt-freeze crust below 1900 m, and a sun crust on south-facing slopes. There could be more than 100 cm on this layer in wind loaded areas.
A crust from early December may be found around 200+ cm deep in the snowpack. In shallow rocky areas, it may still be possible to trigger this layer. In deeper snowpack areas, it appears to be unreactive.
Terrain and Travel
- Keep in mind that human triggering potential persists as natural avalanching tapers off.
- Be aware of highly variable recent wind loading patterns.
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
Avalanche Problems
Wind Slabs
Wind slabs will likely remain reactive to human triggers. Be aware of the potential for wind loading on a variety of aspects including atypical terrain features on southerly aspects due to recent northerly wind.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2
Persistent Slabs
50-100 cm of snow sits on a widespread weak layer that consists of facets, surface hoar, or a crust depending on location. Avalanches may propagate widely on this layer.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1.5 - 2.5