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Avalanche Forecast

Archived

Jan 20th, 2020–Jan 21st, 2020

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

Regions

Kananaskis.

Extensive wind slab formation has occurred. Human triggering is likely.

Confidence

High -

Weather Forecast

The strong SW winds should subside overnight, and be generally light on Tuesday morning. Then in the afternoon the SW flow will pick up strength again, returning to strong by Tuesday evening. Light precipitation is expected through Tuesday and into Wednesday, but unfortunately accumulations will only amount to about 5cm. Temperatures on Tuesday should climb to -4 by early afternoon.

Avalanche Summary

A couple of recent naturally triggered wind slabs up to size 2.5 have occurred on easterly aspects in the Alpine and Treeline elevation bands.

Snowpack Summary

The snowpack is settling with the recent warm weather. Moist snow was observed on sheltered solar aspects at lower elevations today. This should produce a thin crust by tomorrow morning. Due to persistent strong winds and warming temperatures, wind slabs are now widespread at all elevations and on all aspects except westerly. These slabs are of varying thickness and also have highly inconsistent results in snowpack stability tests. Forecasters continue to monitor the Dec 31 layer (surface hoar or facets) that is now buried 50cm on average. The layer has not been particularly active in avalanche activity, but it's a good thing to keep an eye on. The mid-pack is unusually strong and settled for this part of the mountain range. While, in many ways this is a good thing, it also serves to mask the significant basal weakness. There is still potential to trigger the basal layers, particularly in shallow snowpack areas, which could result in very large, destructive avalanches.

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Extra caution is needed around cornices under the current conditions.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.