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Avalanche Forecast

Archived

Dec 17th, 2020–Dec 18th, 2020

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 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.

Avalanche control on Mt Stephen and Bosworth Friday night.

Strong winds and incoming snow will increase the potential for avalanches triggered at upper elevations to run full path in steep areas. Minimize overhead hazard for the next few days!

Weather Forecast

Strong West winds and 10-15 cm of new snow are forecast starting Friday afternoon with similar amounts and wind conditions on Saturday and Sunday. Valley bottom temperatures should stay around -5 with ridge top temperatures around -12 to -15.

Snowpack Summary

Wind slabs forming in the alpine with moderate to strong W winds. 40-60 cm of storm snow at treeline sits over the Dec 13 and Dec 7 layers of sun crust, facets and some surface hoar. The Nov crust/facets exist near the bottom of the snowpack in shallow snowpack areas. Snowpack depths at treeline are between 100-180 cm.

Avalanche Summary

Ski resorts reported small ski-cut and explosive triggered wind slabs and loose dry avalanches up to size 1.5 on Thursday. Weather limited visibility in the alpine and no other natural avalanches were observed or reported. One natural size 2.5 storm snow avalanche was reported off Mt Ogden on Thursday covering ski tracks in the path below. 

Confidence

Timing, track, or intensity of incoming weather system 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.