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Avalanche Forecast

Archived

Feb 11th, 2020–Feb 12th, 2020

Alpine
Natural avalanches possible, human triggered probable.
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

Kananaskis.

Very strong and highly variable winds have changed the picture in the Alpine. Be aware of fresh wind slabs on several different aspects.

Confidence

High -

Weather Forecast

Flurries will end Tuesday evening, with clearing skies arriving on Wednesday. The morning will be cold with temps near -21, but expect -6 by late afternoon. Winds will diminish in speed through the night with only light NW winds expected for most of Wednesday.

Avalanche Summary

Isolated small sluffs in very steep Alpine terrain due to the strong winds. In addition, 2 new slab avalanches were noted today.

1. On a NE aspect at 2400m a naturally triggered shallow wind slab ran for approximately 80m before stepping down to the basal layers. This resulted in a size 2.0 full-depth avalanche.

2. In very steep Alpine terrain on an E aspect a size 1.5 naturally triggered wind slab was observed on the Goat Range.

Snowpack Summary

Trace to 3cm of new snow, brings recent storm snow totals to around 15cm at Treeline. Below 2300m this recent snow remains low density. However, in the Alpine a wide variety of wind slab depths and densities dominate the landscape, from recent strong and gusty NW/W/SW winds. Forecasters experienced some cracking today in wind effected terrain. These surface layers overlie a number of generations of previously formed wind slabs in the Alpine and at Treeline. Near valley bottom the buried rain crust from earlier in the month continues to hold the weight of a skier. Overall, the snowpack has a well settled and strong midpack, but the basal weaknesses persist, particularly in shallow snowpack regions. 

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Be careful as you transition into wind affected terrain.
  • 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.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

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.