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Avalanche Forecast

Archived

Dec 13th, 2021–Dec 14th, 2021

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

Regions

Yukon.

The north wind has formed widespread wind slabs, even in low elevation terrain. The cold will help to reduce the likelihood of triggering these slabs, but we remain wary of steep terrain near ridge crest, convex rollers and other spots that appear to be fat and wind loaded.

Confidence

Low - Uncertainty is due to the extreme variability of wind effect on the snowpack. Uncertainty is due to the limited number of field observations.

Weather Forecast

MONDAY NIGHT: Clear, overnight low temperature around - 30 C, light southwest wind, no new snow expected.

TUESDAY: Broken cloud cover, daytime high temperature around -22, light south wind, no snow expected.

WEDNESDAY: Broken cloud cover, daytime high temperature around -20, light west wind, no snow expected during the day, trace of snow possible Wednesday night.

THURSDAY: Clear skies, daytime high temperature around -22, moderate to strong northwest wind at upper elevations, no snow expected.

Avalanche Summary

No recent avalanche observations to report, it's possible natural wind slab avalanches may have failed during the wind event over the weekend.

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. 

Natural avalanche activity and human triggered avalanches will be most likely in wind-loaded features anywhere recent winds have redistributed the snow. Triggering the deep layer (see the December 1 avalanche described above) is most likely to occur in shallow areas or where the snowpack variable in depth with a mix of shallow and deep zones. 

Snowpack Summary

Northerly winds have gotten into almost all the terrain of the White Pass, even down into the trees at lower elevations. Big thanks to the party who submitted this MIN on Sunday! Lots of shooting cracks were observed as they were out in the Fraser Chutes. Wind slabs are expected to be the principle problem, and It is likely getting pretty hard to find snow that is not wind effected.

The middle snowpack is supportive to travel but snow depth still varies greatly with aspect and elevation. 

A layer of weak, sugary snow at the base of the snowpack has been observed in most areas. This layer was reactive earlier in December, and it might still be possible to trigger this deeply buried layer in shallow snowpack areas or if a cornice fall or surface avalanche impacts a slope. If triggered, this basal layer could produce large avalanches. This sugary layer will likely become weaker in the coming days with cold temperatures potentially making it increasingly sensitive to triggering.

Terrain and Travel

  • Keep your guard up at lower elevations. Wind slab formation has been extensive.
  • 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.