Avalanche Forecast

Issued: Dec 9th, 2012 9:05AM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Storm Slabs, Persistent Slabs and Deep Persistent Slabs.

triley, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Tuesday

Weather Forecast

Overnight and Monday: Light precipitation and moderate Westerly winds overnight are expected to shift to the NW during the day and become gusty up to 60 km/hr. Freezing level should be about valley bottom, and alpine temperature about -7.0Tuesday: Expect the winds to shift to the West as the trailing cold front moves through the region bringing 5-10 mm of precipitation and freezing levels at about 1000 metres. The alpine temperature should be about -6.0.Wednesday: There should be a bit of a dry spell during the day with light NE winds. Alpine temperatures near -10.0

Avalanche Summary

Some natural avalanches that were at least 24 hours old were reported from near Kootenay Pass that were size 2.0 and about 25 cms deep. Near Nelson, explosives control produced size 1.0 soft slab avalanches up to 20 cms deep.

Snowpack Summary

The Kootenays have received over a metre of snow over the past week, with Kootenay Pass seeing the highest amount regionally. Regardless, current surfaces most likely include varying amounts of fairly low density storm snow which override wind slabs that formed earlier in the week. Below the recent storm snow exists a surface hoar layer that was buried at the end of November. Recent tests on this layer show CTM (SP) down 100 cm sliding on surface hoar 4-10 mm in size. Near the base of the snowpack sits the early November rain crust. This layer is most likely to be found in deeper snowpack areas at higher elevations. I'm not aware of any activity on this layer in the KB region; however, deep and destructive releases have been observed in the South Columbia region (directly to the north). Keep this on your radar, especially when traveling in areas at higher elevations that have a smooth ground cover where the existing crust is uniform and consistent. Average snowpack depths at treeline are 130-200 cm. There are significant variations in snowpack structure from one drainage to another. In short, digging down and making your own observations will be critical to safe slope selection.

Problems

Storm Slabs

There is a soft slab on the surface that may stiffen with wind transport over night. These slabs may be triggered by light additional loads like a skier or rider.

The new snow will require several days to settle and stabilize.>Avoid freshly wind loaded features.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

A layer of surface hoar buried at the end of November has been responsible for fairly widespread avalanche activity in some areas. Rider triggering is still likely, especially on convex rolls, and unsupported terrain.

Avoid convexities or areas with a thin or variable snowpack.>Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Deep Persistent Slabs

Deep and destructive releases on the early November crust have been observed in the South Columbia Region. If the Tuesday storm does not make this layer reactive, I think we will remove it from primary concerns.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely

Expected Size

3 - 7

Valid until: Dec 10th, 2012 2:00PM