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Avalanche Forecast

Archived

Dec 9th, 2012–Dec 10th, 2012

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

Regions

South Columbia.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Tuesday

Weather Forecast

Overnight and Monday: Light precipitation and moderate Westerly winds overnight are expected to shift to the NW during the day and become gusty up to 60 km/hr. Freezing level should be about valley bottom, and alpine temperature about -7.0Tuesday:Expect the winds to shift to the NW and become gusty as the trailing cold front moves through the region bringing 15-20 mm of precipitation and freezing levels at about 800 metres. The alpine temperature should be about -8.0.Wednesday:There should be a bit of a dry spell during the day with a chance of very light precipitation and light NW winds. Alpine temperatures near -12.0

Avalanche Summary

Some very soft slabs were released with explosives control up to size 1.5 and heavy sluffing reported from ski cutting.

Snowpack Summary

There is widespread sluffing in the new snow in steep unsupported terrain, but no reports of slab avalanche failures in the storm snow. The late November surface hoar is now buried more than a metre deep and close to 150 cms in some of the snowier areas. This layer has mostly been found between 1700-2000 metres in elevation. There have not been any new reports of avalanches sliding on this layer. The early November rain crust is deeply buried. There was one report of a size 3.0 avalanche that released naturally on this layer in the southern Selkirks. I think we need to keep this problem on the front page through another storm cycle, and see how it reacts to more loading and rapid temperature changes.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.