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Avalanche Forecast

Archived

Dec 21st, 2019–Dec 22nd, 2019

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

Clearing skies and new snow will lure people back into the mountains, but stay out of avalanche terrain and away from the runouts of large paths.

Avalanche control on Mounts Whymper, Simpson, Wardle Sunday.  No activities there during that time. 

Weather Forecast

The end of the storm is coming Saturday night. Temperatures will be in the -10C range Sunday, and winds will be light from the West with a few lingering flurries and cloud. Temperatures will continue to cool through the beginning of next week.

Snowpack Summary

30-70cm of warm, wet snow in the past 48hrs with moderate to strong S/SW winds. Storm slabs have formed at all elevations and aspects. Below the new snow the snowpack structure is generally weak, consisting of facets and depth hoar and a Nov crust up to 2500m. These weak layers are getting overloaded with all of the new snow.

Avalanche Summary

Visibility has been very limited but there have been avalanches up to size 3 in various locations. We suspect a good sized avalanche cycle is occurring.

Confidence

Due to the number and quality of field observations

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.