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Avalanche Forecast

Archived

Dec 15th, 2012–Dec 16th, 2012

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

Kootenay Boundary.

Confidence

Fair - Intensity of incoming weather is uncertain on Monday

Weather Forecast

Overnight and Sunday: Light to moderate Southwest winds should become more westerly overnight and during the day Sunday. Very light precipitation should bring 1-3 cms during the day Sunday. Freezing level is expected to remain close to valley bottom and alpine temperatures should be -7.0.Monday: The next system is forecast to move into the region by Monday morning. Expect moderate precipitation overnight bringing 5-10 cms of snow by morning and another 10-20 cms during the day. Strong Southwest winds are forecast during the storm and the freezing level should remain close to the valley bottom.Tuesday: Cool and unsettled conditions in the wake of Mondays storm.

Avalanche Summary

There was one skier controlled release that was size 2.0 and ran on the late November surface hoar layer (Rossland Range).

Snowpack Summary

Reports from the Kootenay Pass and Whitewater areas are similar. Both areas have about 10-15 cms of loose snow that is bonding to another 20-30 cms of well settled snow below. The late November surface hoar continues to give results in snow profile stability tests. In the Rossland range, the late November surface hoar has not been buried by as much new snow, and continues to give sudden planar results in stability tests (when the bond between the layers fail, it fails suddenly and across the whole block that is being tested). The old surface hoar at the boundary between the slabs has been found to be intact and quite large in this part of the region. This well preserved layer may continue to react to increased loading from users or a new storm load.

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.

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.