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Avalanche Forecast

Archived

Mar 16th, 2023–Mar 17th, 2023

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Below Threshold.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Below Threshold.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Below Threshold.

Regions

Yukon, Tutshi, Wheaton, White Pass East, White Pass West.

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.

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.

Saturday

Early morning snowfall then partly cloudy, accumulation 2 to 5 cm, 20 to 40 km/h east wind, treeline temperature -4 °C.

Sunday

Cloudy 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

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.