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

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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.

Saturday

Early 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.

Sunday

Cloudy 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.

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.