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Avalanche Forecast

Archived

Dec 19th, 2020–Dec 20th, 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 avalanches possible, human triggered probable.
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.

Regions

Little Yoho.

More snow and wind arriving Saturday night. Wind slabs in alpine start zones and gullies have the capacity to entrain facets and run to valley bottom. Know what is above you on Sunday.

Weather Forecast

More snow is on the way, Saturday night, amounting to about 20cm by Sunday morning. Up to 45cm by end of day Tuesday. The wind is also to remain strong from the W -SW through Saturday night, facilitating transport. Temperatures will remain seasonal at -5 in the valley and -15 at the ridge.

Snowpack Summary

Cornices growing and wind slabs forming in the alpine with moderate to strong W winds. 20-50 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 and are weakest in shallow snowpack areas. Snowpack at treeline is between 80-160 cm.

Avalanche Summary

Very little avalanche activity was reported by Lake Louise ski patrollers today. Little activity was noted by the forecasting team up 93N today also. Conversely, patrollers at Sunshine were able to ski cut wind slabs at tree line and above up to size 1.5. They also observed a size 2-2.5 come of Bourgeau Left, a wind slab that entrained facets.

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Sunday

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.