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Avalanche Forecast

Archived

Dec 18th, 2020–Dec 19th, 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.

A storm starting Friday night will increase the hazard. The Moderate rating below treeline is due to the potential for avalanches triggered at upper elevations to run full path in steep terrain. Minimize overhead hazard for the next few days!

Weather Forecast

Strong to extreme west winds and 10-15 cm of new snow are forecast starting Friday night with snowfall tapering off by Saturday morning.  Valley bottom temperatures should stay around -5 with ridge top temperatures around -12 to -16. Winds are expected to remain strong until Monday with an additional 10-15 cm of new snow on Sunday.

Snowpack Summary

Cornices growing and 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 at treeline is between 100-180 cm.

Avalanche Summary

Ski resorts again reported small ski-cut and explosive triggered wind slabs and a couple loose dry avalanches in the alpine up to size 1.5 on Friday. Only a couple small loose dry natural avalanches in steep cliffs were observed.

Confidence

Intensity of incoming weather systems is uncertain on Saturday

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.