Avalanche Forecast

Archived

Dec 2nd, 2021–Dec 3rd, 2021

Alpine

Natural avalanches possible, human triggered probable.

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.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Regions

Yukon.

Careful snowpack evaluation is required to manage a late October facet/crust layer that has shown reactivity in a recent size 2.5 skier-remote avalanche. Be aware that if triggered, wind slab avalanches 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

Thursday night: Flurries, up to 10 cm. Moderate to strong southerly winds. Alpine temperatures around -15 C.

Friday: Light flurries. Moderate southeast winds, shifting southwest in the afternoon. Alpine temperatures drop to -20 C.

Saturday: Winds increasing to strong and shifting to the northwest. Alpine temperatures reach -25 C with light flurries throughout the day.

Sunday: Building high pressure will bring mainly clear skies. Light to moderate ridgetop winds from the west. Alpine temperatures around -20 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 reports! Remember that it is still early season, and we look forward to hearing more this weekend.

Snowpack Summary

Another 5-10 cm of new snow will add to last week's 30 cm of storm snow. This new snow will continue to be transported by moderate to strong southerly winds into wind slabs in the alpine and treeline.

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

Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.