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Avalanche Forecast

Archived

Dec 16th, 2021–Dec 17th, 2021

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

Regions

Yukon.

Strong Southwest wind is expected Thursday night, but we don't think there is much snow available to be formed into fresh slabs. That being said, there might be some fresh wind slabs on north facing terrain Friday. 

Confidence

Low -

Weather Forecast

The wind shifts direction, but it's still cold.

THURSDAY NIGHT: Overnight low temperature around -25, strong southwest wind, trace of snow possible.

FRIDAY: Broken cloud cover, daytime high temperature around -15, moderate southwest wind, trace of snow possible.

SATURDAY: Scattered cloud cover, daytime high temperature around -20, light variable wind, no snow expected.

SUNDAY: Scattered cloud cover, daytime high temperature around -20, light to moderate north/northeast wind, no snow expected.

Avalanche Summary

No recent avalanche observations have been reported.

Several avalanches to size 1.5 were observed on south facing aspects Monday, the result of last weekend's strong north wind event.

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. 

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 which has resulted in quite a bit of wind slab development on south facing features. 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 Sunday. It is 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

  • Watch for areas of hard wind slab on alpine features.
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • 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.