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Avalanche Forecast

Archived

Dec 20th, 2011–Dec 21st, 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.

Snowpack conditions continue to be touchy at all elevations for rider triggered avalanches

Confidence

Good - -1

Weather Forecast

Wednesday/Thursday: A ridge of high pressure building over the province will bring a short lived cool, dry spell. Ridgtop winds are moderate from the NW in the am, switching to W in the afternoon. Freezing levels will be valley bottom Wednesday, rising up to 1500m Thursday-back to valley bottom Thursday night. Friday: Light to moderate snow amounts for today (10-15cm). Strong westerly winds, and freezing levels valley bottom.

Avalanche Summary

A rider triggered avalanche was triggered 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. Numerous natural avalanches up to size 2.5 occurred in the Cariboos on Sunday. 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

Some areas of the North Columbia (Cariboos) received up to 50cm of new storm snow over the past few days. The North and West Monashees received up to 60cms. Strong southwest winds and warm temperatures have created wind slabs on North through East aspects in the alpine and at treeline. The storm slab sits between 50-80 cms and have been naturally reactive. This layer is very touchy and rider triggers are likely. The East and South ranges of the North Columbias have been much drier. 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. This is the mid December surface hoar/facet/crust interface. Some areas have a sun crust in the alpine on steep south and west aspects. There is a rain crust that is buried between 40-55 cm in some areas that reaches up to about 2200 metres. 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 long dry spell. Tests show that it is getting harder to pull the snowpack apart at this interface. We may still see this layer become active again if we get the right combination of load and warm temperatures. The midpack is well settled. 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.