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Avalanche Forecast

Archived

Dec 5th, 2021–Dec 6th, 2021

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

Regions

Yukon.

The best travel plans for Monday will avoid convexities and sharp changes in terrain where it may still be possible to trigger old wind slabs. Take note of the current snow surface and let us know what you find, this is what all of Tuesday's storm snow will rest on.

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

Status quo for Monday, but then it’s game on Tuesday as a potentially powerful storm sweeps into the area. Snow amounts are hard to pin down for Tuesday, but we could see as much as 50 cm of new snow. Stay tuned for more details as the storm gets a bit closer.

SUNDAY NIGHT: Temperature around -20 C, moderate to strong west/southwest wind, no significant snowfall expected.

MONDAY: Flurries, temperature around -20 C, moderate to strong southwest wind, 1 to 5 cm of snow expected during the day with another 1 to 5 cm likely Monday night.

TUESDAY: Snow, becoming heavy early Tuesday morning, potential for as much as 50 cm by Tuesday night, strong to extreme southwest wind.

WEDNESDAY: Broken cloud cover, daytime high temp around -10 C, light southwest wind, trace of snow possible.

Avalanche Summary

Some hardy Yukoners were out skiing Sunday and were kind enough to post a MIN of what looks to be a great day on snow despite the cold temps, more details here.

Avalanche control work on Saturday produced many large wind slab avalanches on NE facing features around 1700 m. Most of these avalanches stepped down to weak facets and rocks.

Lots of whumping and cracking have been reported across the region, a product of our shallow early-season snowpack which includes wind slabs and a weak facet/crust layer at the base of the snowpack.

On Tuesday, a size 2.5 skier-remote persistent slab was reported on the MIN (see report here). The avalanche was triggered from around 100m away, by a group of 5 riders on an east aspect at 1400m. The avalanche was suspected to have failed on an early-season facet/crust layer.  

Snowpack Summary

Varied wind directions in the past week have created a mix of old and new wind slabs everywhere. Expect these wind slabs to be quite stiff in the current cold temps.

Snow depth at treeline is approximately 80-120 cm, depths in the alpine range from 100-200 cm.

A facet/crust layer can be found near the bottom of the snowpack. This layer was reactive to human triggering last week with a notable skier-remote avalanche on November 30th.

Terrain and Travel

  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Be careful as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.