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Avalanche Forecast

Archived

Jan 23rd, 2020–Jan 24th, 2020

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

Regions

Little Yoho.

Forecasters confidence in the snow-pack is low. There is lots of good skiing but careful assessment of bigger slopes is still required. Natural avalanche activity has subsided, however human triggered avalanches are still possible.

Weather Forecast

Mixed sun and cloud for Friday with only light flurries along the divide. Freezing levels will rise to 1800 m on Friday and then return to surface for the weekend. Alpine winds will be in the moderate range out of the SW.

Snowpack Summary

Fresh wind slabs (up to size 1.5) can be found near ridge-tops. There is 40-60 cm above the Dec 31 layer of facets, surface hoar and sun crust which is slowly becoming less reactive. In most areas in Little Yoho the lower pack is well settled. Shallower snow-pack areas will see a weaker lower pack.

Avalanche Summary

No new natural avalanches observed over the past few days. Explosive control Tuesday on highway 93 North produced varied results. Much of the control work produced smaller then expected results, though one large size 3.5 was triggered on the deep persistent problem.

Confidence

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.