Avalanche Forecast
Regions:
The snowpack will need time to strengthen after the intense storm. Large human-triggered avalanches will be very likely. Travel in avalanche terrain is not recommended.
Confidence
Moderate
Avalanche Summary
We expect a natural avalanche cycle occurred over the day on Thursday during periods of rapid loading. Natural activity could continue into Friday with more snow and wind. Human triggering is very likely given the amount of new snow and what it is resting on. Avoidance of avalanche terrain is recommended until the snowpack has time to adjust.
Snowpack Summary
Thursday's substantial storm dropped upwards of 50 cm of snow around the Haines Pass with rain falling on top of the snow up to 700m, amounts tapered as you move inland.
Southerly wind accompanied the storm, meaning deeper deposits may exist in lee terrain features near ridges. All this snow overlies previously wind affected snow (sastrugi) in wind affected areas and faceted snow in sheltered features. The new snow may not bond well to these previous surfaces.
The storm snow is also loading a buried weak layer of surface hoar found about 80 cm to 200 cm around around Haines pass. This layer is most prominent on northerly slopes sheltered from the wind. On other aspects, this layer is a hard melt-freeze crust with weak facets around it. To date this layer is has been most problematic in alpine terrain.
The remainder of the middle of the snowpack is consolidated and strong. Weak faceted grains are found near the base of the snowpack and a thick melt freeze crust is next to the ground up to 20cm thick.
Weather Summary
Thursday Night
Cloudy with snowfall, accumulation 10 to 20 cm, 40 to 60 km/h south wind, treeline temperature -5 °C.
Friday
Cloudy with snowfall then clearing, accumulation 5 cm, 20 to 40 km/h south wind, treeline temperature -5 °C. Freezing level 700 m.
SaturdayEarly morning snowfall then a mix of sun and cloud, accumulation 2 to 5 cm, 40 to 50 km/h southeast wind, treeline temperature -2 °C. Freezing level rising to 1000 m.
SundayCloudy with snowfall, accumulation 2 to 5 cm, 30 km/h south wind, treeline temperature -5 °C. Freezing level 600 m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Travel in alpine terrain is not recommended.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Be aware of the potential for large, deep avalanches to run full path or even longer.
Avalanche Problems
Storm Slabs
A substantial storm impacted the region on Thursday, with more snow expected Thursday night. Storm and wind slabs likely rapidly formed and they may not bond well with previous surfaces. Human triggering will remain very likely for Friday.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Very Likely
Expected Size: 1 - 2.5
Persistent Slabs
The new snow is loading a weak layer of surface hoar and/or faceted grains around a hard crust, which increases the likelihood of triggering an avalanche on this layer. The layer is buried around 80-200 cm and has previously produced widely propagating avalanches in alpine terrain and it is capable of being remotely triggered from a distance. The most likely area for riders to trigger it is in wind-sheltered, north-facing terrain, and in rocky terrain where the snowpack is thin.
Aspects: All aspects.
Elevations: Alpine.
Likelihood: Possible - Likely
Expected Size: 2 - 3