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Avalanche Forecast

Archived

Dec 20th, 2018–Dec 21st, 2018

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

Regions

Kananaskis.

We do not have a trustworthy snowpack at the moment. Steep treeline features (I.E. Tryste Chutes) are especially suspect. Runs that are normally "good to go", should be treated with caution and respect.

Confidence

High.

Weather Forecast

Snow tapering off tonight. Totals could be as much as 10cm. Alpine winds will remain moderate to strong from the west with temperatures falling to -12°c by tomorrow afternoon. Long term, we are expecting only flurries with mostly cloudy skies. Another pulse is possible by early next week.

Avalanche Summary

It turns out the cycle reported yesterday was more widespread than we originally thought. We saw many size 2 avalanches today at treeline with impressive propagations. Large alpine paths have also run. It appears that any aspect from North to South is suspect lately. In all cases, the Dec 10th facets are to blame. Be extremely cautious with any slope that hasn't slid.

Snowpack Summary

More snow arrived last night and today. We now have 40-70cm on top of the Dec 10th facet layer at treeline. Winds have continued to howl from the west today. The alpine is either wind scoured, or windslabs. Treeline also has these wind slabs, however they not as dense, which makes them tougher to predict in terms of "triggerability". A profile today at 2000m had the Dec 10th down about 40cm. There were repeatable test results (compression test 19, sudden collapse) on this layer indicating it is a serious concern. The bottom line? We have several very weak layers lingering in the lower snowpack with a windslab sitting on top. Basically a house of cards waiting to reach the tipping point.

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.