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Avalanche Forecast

Archived

Dec 17th, 2012–Dec 18th, 2012

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

Regions

Banff Yoho Kootenay.

Conditions are good for December. However, it is still early season and many of the bigger alpine features have not had a chance to fill in yet. Many thin spots still exist in the alpine leading us to have lower confidence in these features.

Weather Forecast

The drought continues...  Temperatures are cooling off a bit (approaching -20 along the divide).  We might see a couple cm's on monday night/ tuesday, and then a clearing trend for wednesday. ALP winds are forecast to increase to Moderate from the W tonight with the passing of a low pressure system and then ease again on Tuesday.

Snowpack Summary

A couple cm's of fluff overlies a well settled snowpack. In the ALP, old windslabs exist and are visible as 'rippled' snow on the surface. These may be reactive to human triggering. The Nov. 6th crust is facetting out, and is now more of a facet layer than a crust in many places. This layer is giving hard to no results in compression tests.

Avalanche Summary

No new avalanches observed today by forecasters during a flight of the highway avalanche control paths as well as a team in the Lake O'hara area.

Confidence

Wind speed and direction is uncertain on Monday

Problems

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.