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Avalanche Forecast

Archived

Dec 19th, 2019–Dec 20th, 2019

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

Regions

Banff Yoho Kootenay.

High snowfall amounts and strong winds will elevate the avalanche hazard for the next few days.

Avoid overhead hazard and avalanche terrain.

Weather Forecast

The infamous 'atmospheric river' (I wonder who coined that term??) is flowing through our region for the next two days. Forecasts along the Divide predict snow accumulation up to 25cm on Friday, 25+cm on Saturday and another 10cm by Sunday morning. Temperatures will rise as the freezing level reaches 1600m. Winds will be strong from the SW.

Snowpack Summary

Recent strong winds have formed wind slabs in the alpine and exposed tree line areas. The snowpack structure is generally weak, consisting of facets and depth hoar and will be stressed by the incoming storm snow. The Nov crust is present up to 2500m and ~30 cm up from ground. Snowpack depths at treeline range from 80-160 cm.

Avalanche Summary

No new natural avalanche activity in the past few days, though there have been reports of skier triggered wind slabs up to sz 1.5.

Explosive avalanche control at local ski areas have produced sz 1.0 windslabs in steep, wind loaded areas.

Confidence

Intensity of incoming weather systems is uncertain on Friday

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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.