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Avalanche Forecast

Archived

Jan 8th, 2021–Jan 9th, 2021

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Rockies.

  

Sporadic large natural persistent slab avalanches have recently been reported in this region. This low likelihood, high consequence scenario is best avoided by choosing conservative terrain away from overhead hazard.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

  

FRIDAY NIGHT: Clear / Light, southwest ridgetop wind / alpine low temperature -18 / Freezing level valley bottom.

SATURDAY: Mix of sun and cloud / Light, southwest ridgetop wind / alpine high temperature -9 / Freezing level valley bottom.

SUNDAY: Mix of sun and cloud / Moderate, west ridgetop wind / alpine high temperature -8 / Freezing level valley bottom.

MONDAY: Mostly cloudy / Moderate, northwest ridgetop wind / alpine high temperature -6 / Freezing level 1200 m.

Avalanche Summary

A large (size three) cornice triggered persistent slab avalanche was reported on a large south facing alpine slope in the Crowsnest Pass area on Thursday. This ia an example of the "low probability; high consequence" scenario that persistent slab problems often create. MIN report HERE.

Explosive avalanche control produced a few size 2-3 wind slab avalanches on Tuesday. Last weekend there were numerous natural size 2-3 slab avalanches. Most of these were storm slab avalanches in alpine terrain, although some of the reports from the upper Elk Valley included avalanches at treeline elevations that likely failed on 60-100 cm deep surface hoar layers.

Snowpack Summary

Lingering wind slabs formed by recent snow and wind remain possible to human trigger in isolated areas. The upper snowpack consists of several layers of old wind slabs, while the lower snowpack consists of decomposing crusts and weak faceted snow. In the Elk Valley a decomposing surface hoar layer can be found around one of these crusts 50-100 cm below the surface. Avalanche activity on these layers in the lower snowpack have been sporadic, mostly occurring during natural avalanche cycles. However, this snowpack structure is always a concern for human triggering; especially on steep, rocky slopes with a shallow or thin to thick snowpack.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried weak layers.
  • Avoid exposure to slopes that have cornices overhead.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.