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Avalanche Forecast

Archived

Jan 17th, 2021–Jan 18th, 2021

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

Dig down and investigate deeper layers in the snowpack before committing to big lines.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

SUNDAY NIGHT- Mostly cloudy / Moderate to strong west-northwest wind / Alpine high temperature near -5

MONDAY - Sun and cloud / Light northwest wind / Alpine high temperature near -6

TUESDAY - Cloudy with isolated flurries / Increasingly strong southwest wind / Alpine high temperature near -9

WEDNESDAY - Cloudy with sunny breaks / moderate to light west wind / alpine high temperature near -7

Avalanche Summary

On Thursday, explosives triggered a size 2.5 wind slab avalanche, and one natural size 3 persistent slab avalanche, both occurred on southeast aspects in the alpine.

Additionally on Thursday, a size 3 persistent slab avalanche was reported on an east aspect at 2400 m in the neighboring Waterton National Park region.

On Wednesday, were several natural avalanches to size 2.5 were observed and explosives also triggered avalanches up to size 2.5.

And just over a week ago (Jan 14), a natural size 3 persistent slab avalanche was reported on a large south-facing alpine slope in the Crowsnest Pass area.

These recent avalanches are a prime example of the "low probability; high consequence" scenario that persistent slab problems often create. 

Snowpack Summary

Strong winds have polished and pressed snow into hard slabs and sastrugi and stripped windward slopes. A melt-freeze crust covers surfaces up to 1850 m.

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 60-120 cm below the surface. Avalanche activity on these layers in the lower snowpack has been sporadic, mostly triggered by large loads such as a wind slab avalanche, or a cornice fall. These deeper weak layers are most likely to be human triggered on steep, rocky slopes with a shallow or thin to thick snowpack.

Terrain and Travel

  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Be alert to conditions that change with elevation, aspect and exposure to wind.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

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.