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Avalanche Forecast

Archived

Dec 3rd, 2021–Dec 4th, 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 possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Below Threshold.

Regions

Yukon.

A facet/crust layer at the base of the snowpack has shown reactivity in a recent size 2.5 skier remote avalanche. Cold temperatures will decrease the reactivity of wind slabs, but if triggered wind slabs may step down to this deeper layer resulting in larger avalanches. 

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

Friday overnight: A mix of sun and cloud with trace amounts of new snow. Light northwesterly winds and alpine temperatures around -20 C. 

Saturday: Flurries with trace accumulation. Light to moderate northerly winds with alpine temperatures dropping to around -25 C. 

Sunday: Mainly cloudy with flurries. Up to 2 cm of new snow accumulation. Moderate winds from the southwest increase to strong in the afternoon. Temperatures increase throughout the day, reaching -15 in the evening.

Monday: A cloudy day with strong southerly winds. 3-10 cm of new snow throughout the day with alpine temperatures rising to -5 C. 

Avalanche Summary

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. 

Lots of whumping and cracking have been reported across the region, which is most likely associated with an early-season shallow snowpack, wind slab formation, and a weak facet/crust layer at the base of the snowpack. 

Thank you for the all informative and detailed Mountain Information Network (MIN) reports! Remember that it is still early season, and we look forward to hearing more this weekend.

Snowpack Summary

Northerly outflow winds may create reverse loading in the alpine and treeline. Due to varied wind directions in the past week, expect to find a mix of old and new wind slabs on all aspects alpine and treeline. Expect these wind slabs to be stiffening with a significant drop in temperatures overnight on Friday. 

Snow depth at treeline is approximately 80-120 cm, depths in the alpine range from 100-160 cm.

A facet/crust layer can be found near the bottom of the snowpack. This layer has been reported as being reactive to human triggering in the past week, with a notable skier-remote avalanche on Tuesday.

Terrain and Travel

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

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.