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Avalanche Forecast

Archived

Dec 10th, 2021–Dec 11th, 2021

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

Regions

Yukon.

Weak, sugary crystals exist at the base of the snowpack. Try to stay where the snow is deep and manage overhead hazard diligently. New snow is likely to form relatively short-lived wind slabs.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

FRIDAY NIGHT: mostly cloudy skies, 2-4cm of snow, wind moderate tapering to light from the southwest, temperature -10 C at highway elevation. 

SATURDAY: mostly cloudy in the morning with periods of clearing in the afternoon, no significant precipitation, light wind from the south in the morning changing to moderate wind from the north in the afternoon, -12 C in the morning decreasing to -15 C in the afternoon

SUNDAY: Partly cloudy skies, no precipitation, moderate wind from the north, temperature -21 C. 

MONDAY: Partly cloudy skies, no precipitation, moderate wind from the north, temperature -23 C 

Avalanche Summary

Explosive control earlier in the month produced many large avalanches that failed on the weak sugary crystals at the bottom of the snowpack. These avalanches ran full path.

On December 1, a size 2.5 avalanche was remotely triggered by a recreational group on Log Cabin. This avalanche likely failed on the weak, sugary snow at the bottom of the snowpack.

On Saturday, the most likely avalanche activity will be in wind-affected areas on exposed treeline features and high alpine features. 

Snowpack Summary

Up to 50cm of recent fresh powder snow will be redistributed by moderate south and then north winds over the weekend. Snow quality will be best in sheltered treeline and sheltered, low angled alpine features. The middle snowpack is supportive to travel but snow depth still varies greatly with aspect and elevation. In most places, the entire snowpack sits on top of a layer of weak, sugary snow at the base of the snowpack. This deeply buried layer will likely become weaker over time with cold temperatures starting on Sunday. This is our main layer of concern and, if triggered, could result in large avalanches. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be alert to conditions that change with elevation and wind exposure.
  • Approach lee and cross-loaded slopes with caution.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • 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.