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Avalanche Forecast

Archived

Dec 31st, 2019–Jan 1st, 2020

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 possible, human triggered probable.
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.

Regions

Little Yoho.

The avalanche hazard is increasing with the arrival of new snow and wind. We also have a lot of uncertainty about where the deep persistent layer might be triggered. As a result it is a good time to be patient and make conservative terrain choices.

Weather Forecast

A series of small systems will deliver 5-10cm a day until Friday. Winds will remain in the moderate range, gusting to strong from the SW. Temps will rise slightly on Wednesday with an Alpine high of -4 and a freezing level to 1600m.

Snowpack Summary

New snow and moderate SW winds are creating new wind slabs in lee areas at and above treeline. In most areas the upper snowpack of denser snow sits over a weak mid and lower snowpack consisting of facets, depth hoar and crusts. In deeper snowpack areas these weaknesses are less pronounced. Snowpack depths at treeline average 100-160+ cm.

Avalanche Summary

No new natural avalanches observed or reported. Explosive control at local ski areas produced sz 1 wind slabs in immediate lees on Tuesday. Reports of whumpfing, as well as explosive and skier triggered avalanches up to size 2 on the deep persistent layer have occurred in the past week, we expect this layer to continue to be problem for a while.

Confidence

Intensity of incoming weather systems is uncertain on Wednesday

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.