Avalanche Forecast

Archived

Mar 13th, 2023–Mar 14th, 2023

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Below Threshold.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Below Threshold.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Below Threshold.

Regions

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

Both wind slabs and persistent slabs may linger in alpine terrain.

Confidence

Moderate

Avalanche Summary

Riders observed many old loose and wind slab avalanches over the weekend, predominantly starting in alpine terrain and on southerly slopes.

The latest persistent slab avalanche report was from a week ago where riders remotely triggered the layer from a ridgetop, but snowpack test results indicate this layer could still be triggered and form large avalanches.

Snowpack Summary

Wind affected snow and wind slabs are found in exposed terrain, whereas soft snow may be found in wind-sheltered features, particularly at treeline elevations. The wind has shifted direction, meaning wind slabs may be found on all aspects.

There is a surface hoar layer buried about 60 cm deep in Powder Valley, Tutshi, and Paddy Peak areas and up to 140 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. This layer is has been most problematic in alpine terrain.

The middle of the snowpack is consolidated and strong. Weak faceted grains are found near the base of the snowpack.

Weather Summary

Monday Night

Partly cloudy with no precipitation, 10 km/h northeast wind, treeline temperature -18 °C.

Tuesday

Partly cloudy with no precipitation, 10 km/h east wind, treeline temperature -16 °C.

Wednesday

Mix of sun and cloud with afternoon flurries, accumulation 1 to 3 cm, 20 to 30 km/h south wind, treeline temperature -11 °C.

Thursday

Cloudy with snowfall, accumulation 20 to 30 cm, 60 km/h south wind, treeline temperature -3 °C, freezing level 1000 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Carefully evaluate steep lines for wind slabs.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
Seek out sheltered terrain where new snow hasn't been wind-affected.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.