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Avalanche Forecast

Archived

Feb 22nd, 2012–Feb 23rd, 2012

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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

Kootenay Boundary.

Confidence

Fair - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

A ridge of high pressure is expected to move into the region overnight. Northwest winds are expected to continue to be gusty and strong in the alpine and at treeline on Thursday. Some moisture that will remain in the area is expected to cause periods of moderate precipitation alternating with periods of thin cloud. Continued high pressure is forecast for Friday morning, before a low pressure system moves into the region from the Pacific in the afternoon. Southwest wind and moderate precipitation is forecast to begin in the late afternoon or early evening. Snow and wind should continue overnight and into Saturday. The freezing level is expected to drop down to near valley bottoms on Wednesday night, and then rise to about 1000 metres on Thursday.

Avalanche Summary

We are getting reports of more frequent and larger avalanches that are running on the Feb. 8th crust and/or buried surface hoar. Avalanches up to size 3.0 were reported from the control work at Kootenay pass along the highway corridor. Remotely triggered avalanches continued to be reported. Strong winds are transporting snow into a slab above the weak layers

Snowpack Summary

Another 10-15 cm combined with very strong northwest winds has added to the 30-60 cm of snow that is sitting on top of a highly reactive persistent weak layer (PWL), comprising large surface hoar in sheltered areas and a sun crust on solar aspects. This PWL is now right at the critical depth where triggering is very likely and resulting avalanches could easily be large enough to bury, injure or kill a person. Professionals throughout the region are treating this layer with extreme caution, since it is showing signs of remote triggering and the ability to propagate in low angled terrain. Alpine winds have been strong enough to blow snow around, adding a touchy wind slab problem into the mix behind exposed terrain features in the alpine. In shallow snowpack areas concerns remain for the mid-December persistent weakness down around 80-100cm and for basal facets. Treeline snowpack depths are approximately 230 cm.

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.