Avalanche Forecast
Issued: Mar 16th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
mconlan,
Avalanche Canada
The snowpack will need time to strengthen after Thursday's intense storm. Human-triggered avalanches will be very likely and sunny skies could trigger natural avalanches. Travel in avalanche terrain is not recommended.
Summary
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 followed by sunny conditions. Human triggering is very likely given the amount of new snow and what it is resting on. Natural avalanche activity could continue during periods of intense sun or wind loading. Avoidance of avalanche terrain is recommended until the snowpack has time to adjust.
Snowpack Summary
Thursday's substantial storm dropped around 50 cm of snow around White Pass, with lesser amounts as you move east. 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 deep in Powder Valley, Tutshi, and Paddy Peak areas and approximately 150 to 200 cm around White 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, particularly in thin snowpack areas.
Weather Summary
Thursday Night
Cloudy with snowfall, accumulation 10 to 20 cm, 40 to 60 km/h south wind, treeline temperature -5 °C.
Friday
Mostly clear skies with no precipitation, 20 to 40 km/h south wind, treeline temperature -5 °C.
SaturdayEarly morning snowfall then partly cloudy, accumulation 2 to 5 cm, 20 to 40 km/h east wind, treeline temperature -4 °C.
SundayCloudy with light snowfall, accumulation 1 to 3 cm, 30 km/h south wind, treeline temperature -5 °C.
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.
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. Sunny skies could also quickly destabilize the snow on sun-exposed slopes, forming natural avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
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 cm in the eastern portions of the region and up to 200 cm around White Pass. This layer 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
Expected Size
Valid until: Mar 17th, 2023 4:00PM
