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Avalanche Forecast

Archived

Dec 11th, 2021–Dec 12th, 2021

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

Regions

Little Yoho.

New snow and strong winds have increased the avalanche hazard at all elevations for Sunday.

Weather Forecast

This storm should bring another 10-15 cm overnight before moving out of the region early Sunday morning with only light flurries remaining. Temperatures will drop following the storm. Expect to see highs of -12 to -15 C at treeline on Sunday. Wind speeds will also drop into the moderate range out of the SW in most areas with some strong gusts.

Snowpack Summary

Up to 15 cm of new snow Saturday with more expected overnight. 25-45 cm of snow now overlays the Dec 2 crust which is present up to 2100-2250 m. At treeline and above, strong to extreme W & SW winds have developed slabs in lee areas with extensive wind effect in open areas. The weak Nov 5 crust/facet interface is present near the ground.

Avalanche Summary

Several skier and explosive controlled wind slab avalanches up to size 2 were reported by the local ski areas along with some smaller dry loose avalanches. A few other reports of small skier triggered wind slabs and natural sluffing in steep terrain were also received.

Confidence

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

Problems

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.

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.

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.