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Avalanche Forecast

Archived

Dec 21st, 2011–Dec 22nd, 2011

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

Regions

Cariboos.

Confidence

Good - -1

Weather Forecast

Thursday: Mainly dry, clearing conditions. Flurries expected in the evening. Ridgetop winds blowing 50km/hr from the north-west. Treeline temperatures near -10. Friday: Switching to a zonal westerly flow. Dry and cold. Treeline temperatures near -15. Saturday: Freezing levels may may rise to 1500m, with light to moderate snow.

Avalanche Summary

On Tuesday a skier triggered an avalanche remotely 20m away. This was on a NE aspect at 2100m and was a size 2. Remotely triggered avalanches are an indicator of a very touchy snowpack. You need to be very aware and make observations while you travel in avalanche terrain at all elevations. They ran on all aspects above 1800m. Most of this avalanche activity has occurred on the early December surface hoar/facet/crust layer.

Snowpack Summary

The North Columbia (Cariboos) received up to 50cm of new storm snow over the past few days. Strong southwest winds and warm temperatures have created wind slabs on North through East aspects in the alpine, treeline, and below treeline. The storm slabs are between 50-80cms and sit on the mid December surface hoar/facet/crust interface. This interface has been very active; especially to rider triggers. Some areas have a sun crust in the alpine on steep south and west aspects. There is a rain crust that is buried between 40-55cms in some areas that reaches up to about 2200 metres. The new snow load continues to build faster in the northern ranges than in the southern and eastern ranges. The depth of the new storm snow above the various old surfaces is what is driving the danger ratings at this time. The problems that exist are found in the upper meter of the snowpack. The mid-pack is reported as generally strong and well settled. Observers are still able to find the early November surface hoar layer that sits around 120-150cms down. This layer has not been reactive during the recent loading after our 2 week dry spell. It may be time to put this layer to bed. Going down deeper sits the interface between the snow that did not melt over the summer, the glacial ice, and the October rain event. At this point the interface remains dormant.

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.

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.