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Avalanche Forecast

Archived

Dec 28th, 2014–Dec 29th, 2014

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 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

Purcells.

Avalanche danger is expected to remain at Considerable during the forecast cold and clear weather for the end of the year.

Confidence

Fair

Weather Forecast

Gradually clearing overnight with light Northeast winds and alpine temperatures dropping down to about -22. Mostly clear and cold on Monday with light to moderate Northeast winds and alpine high temperatures around -20. Clear and cold on Tuesday with light Northwest winds. Continued clear and cold on Wednesday.

Avalanche Summary

No natural avalanches reported. Explosives control work resulted in avalanches up to size 1.5 that appear to have run on the mid-December surface hoar that is buried down 40-60 cm.

Snowpack Summary

Some areas may have a thin layer of surface hoar that was buried on December 27th and now has about 5-10 cm of light dry snow above. The slab above the persistent weak layer of surface hoar and crust that was buried in mid-December is now 40-60 cm thick and gives mostly sudden planar results in snow profile tests when moderate forces are applied. The persistent slab problem is widespread across the region and is not expected to improve it's bonding properties during the forecast dry and cold weather. Shallow snowpack areas continue to have concerns for a deeper early season crust/facet layer down more than a metre that may collapse under large loads or from weak trigger spots around exposed rocks and/or trees.

Problems

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.