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Avalanche Forecast

Archived

Dec 29th, 2019–Dec 30th, 2019

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

Regions

Banff Yoho Kootenay.

With winds forecast to increase late Monday and some potential for  snow, be wary of the potential for an up-tick in natural activity into Tuesday. Continue to avoid exposure to overhead avalanche terrain and select modest angled slopes for travel.

Weather Forecast

Cloud cover will increase Monday as warmer air approaches. A mild inversion may remain until midday as winds rise to strong in the alpine, possibly arriving with small amounts of snow. Into Tuesday, and through Wednesday, a series of systems will reach the forecast region with light snowfall. Winds look like they will diminish late Tuesday.

Snowpack Summary

Moderate to strong W and SW winds have redistributed snow in the alpine and the upper areas of treeline. Snowpack depths at treeline range from 100 to 160cm. The Nov crust is found ~ 30cm above the ground and is present up to 2500m. Weak facets below this depth are the obvious weakness and are more developed in shallow areas.

Avalanche Summary

Recent reports of skier triggered avalanches within the region and reports of whumphfing on the deep persistent layer have continued in the last 48 hrs. Explosive avalanche control at ski areas today produced a few sz 1-2 windslabs in steep, wind loaded areas as has been seen over the last few days with a few  of these stepping down to the facets.

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Tuesday

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.

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.