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Avalanche Forecast

Archived

Jan 31st, 2020–Feb 1st, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
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.

Avoid all avalanche terrain Saturday. With the incoming storm, we expect the natural avalanche activity to increase. Some will run well into the valley bottom, and possibly to the end of the paths.

Weather Forecast

Overnight Friday, we expect 20-30cm (highest amounts Lake Louise and North) and another 30-50cm on Saturday with strong to extreme winds & 2000m freezing levels. These warm temperatures will mean rain at lower elevations. The storm passage mid-day Saturday is marked by dropping temperatures (to -15-20C), decreasing wind, and tapering snow amounts.

Snowpack Summary

Wind and storm slabs are developing over the next 24 hours with strong SW wind, 40-80 cm of snow, and rain below 2000 m. We expect this to overload the Dec 31 layer of facets, surface hoar and sun crust (currently down 40-80 cm) and/or the deep persistent basal layer. Loose wet avalanches are likely below tree line Saturday morning.

Avalanche Summary

Visibility has been obscured as the "atomospheric river" storm moved into the region this afternoon. We expect natural avalanches to be occurring for the next 24 hours with the onset of wind, snow, rain, and rising temperatures.

Confidence

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.