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Avalanche Forecast

Archived

Dec 12th, 2021–Dec 13th, 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, human triggered possible.
Below Treeline
Below Threshold.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Below Threshold.

Regions

Yukon.

If you're heading out into the cold you're going to want to seek out wind sheltered terrain where you can avoid fresh wind slabs.

Confidence

Low - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Brrrrrrr!

SUNDAY NIGHT: Low temperature around -26 C, light to moderate outflow winds out of the northeast, most prominent at lower elevation, no snow expected. 

MONDAY: Broken clearing to scattered cloud cover in the late afternoon, daytime high temperature around - 20 C, light variable wind, no new snow expected.

TUESDAY: Clear skies at dawn with cloud cover increasing after lunch, daytime high around -16, light to moderate south/southwest wind, no snow expected.

WEDNESDAY: Broken cloud cover, wind light southwest in the early morning steadily increasing to moderate west southwest in the afternoon, light flurries possible after lunch.

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. 

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

Low density snow from the last storm is being redistributed by winds that were at first southerly then switched to north, then northeasterly, now northwesterly. Old wind slabs on northerly aspects are likely becoming less sensitive, but expect new wind slabs on south, southwest and southeast aspects. Snow quality will be best in sheltered areas, which is also where you are least likely to find wind slab problems. 

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 increasingly cold temperatures potentially making it increasingly sensitive to triggering.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • 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.