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Avalanche Forecast

Archived

Dec 19th, 2021–Dec 20th, 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, 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.

Small wind slabs likely exist in extreme terrain near ridge crest. Avoid areas where the snowpack goes from thick to thin as we have a lingering deep persistent slab avalanche problem that can't be totally ruled out.  

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

SUNDAY NIGHT: Overnight low temperature around -22, light north/northwest wind, no snow expected.

MONDAY: A few clouds, daytime high temperature around -15, moderate to strong west/northwest wind, no snow expected during the day, 3 to 6 cm possible Monday night.

TUESDAY: Overcast, daytime high temperature around -10, strong north/northeast wind, 2 to 6 cm of snow possible.

WEDNESDAY: Broken cloud cover, daytime high temperature around -15, strong north wind, no snow expected.

Avalanche Summary

This MIN from Saturday shows a small wind slab in a terrain feature known for producing these kinds of avalanches. Other than that, we haven't had any recent avalanche observations, it was pretty quiet and beautiful in the White Pass this weekend. 

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. 

Snowpack Summary

There's been a glorious inversion in place, and small surface hoar is forming in the valley fog.

The White Pass is looking heavily wind effected, as evidenced in this MIN. Recently winds have been out of the southwest and northwest. Wind slabs are almost always present in the mountains, watch for small wind slabs immediately lee of ridge crest.

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 has been inactive since early December, but it might still be possible to trigger this deeply buried layer in shallow snowpack areas. A cornice fall or surface avalanche impacting a slope may also have the potential to trigger it.

Terrain and Travel

  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

Problems

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.