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Avalanche Forecast

Archived

Jan 19th, 2021–Jan 20th, 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.

Look for pockets of loose snow in sheltered terrain. Dig down and investigate deeper layers before committing to big features.

Confidence

Moderate - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

TUESDAY NIGHT- Cloudy / Strong southwest wind, 30-60 km/h / Alpine low temperature near -10

WEDNESDAY - Cloudy with sunny breaks / Southwest wind, 20-40 km/h / Alpine high temperature near -8

THURSDAY - Sunny with clouds / Northeast wind, 10-20 km/h / Alpine high temperature near -10

FRIDAY - Sunny / Northeast wind, 10-25km/h / alpine high temperature near -9

Avalanche Summary

Last Thursday (Jan 14), 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, a natural size 3 persistent slab avalanche was reported on a large south-facing alpine slope in the Crowsnest Pass area and a size 3 persistent slab avalanche was reported on an east aspect at 2400 m in the neighboring Waterton National Park region.

The day prior (Wednesday, Jan 13), several natural avalanches to size 2.5 were observed and explosives also triggered avalanches up to size 2.5.

Avalanche activity has dropped, however these recent avalanches are a prime example of the "low probability; high consequence" scenario that persistent slab problems often create. 

Snowpack Summary

A variety of wind affected surfaces covers upper tree line and alpine terrain. A polished crust is found up to 1800 m and higher on solar slopes.

Soft pockets of redistributed snow may hide in sheltered areas.

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 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.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.