Avalanche Forecast

Issued: Dec 8th, 2012 9:34AM

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

swerner, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Timing of incoming weather is uncertain

Weather Forecast

Sunday:Â Warm front reaches the Interior. Snow amounts 5-10 cm, ridgetop winds W 20 km/hr , alpine temps near -5, freezing levels at 500 m.Monday: Trace of new snow, ridgetop winds W 20 km/hr, alpine temps near -6, freezing levels 900 m.Tuesday: The cold front is expected to slide down from the North bringing moderate snow fall amounts, ridgetop winds SW 30 km/hr, alpine temps near -8, freezing levels near 1000 m.

Avalanche Summary

Recent explosive control work triggered several 1.5-2.0 slab avalanches on SE-SW aspects 1700 m and above. These avalanches failed on the early December crust, that recently got buried. Please don't confuse this with the early November facet/crust layer that sits near the base of the snowpack.Any observations from the field are welcome at forecaster@avalanche.ca.

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

Varying amounts of new snow are likely to produce soft slab and loose snow avalanches. The weight of these avalanches may even trigger weak layers that exist deeper in the snowpack. Rider triggers are likely.

Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>Be cautious of sluffing in steep terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

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.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 5

Deep Persistent Slabs

Deep and destructive releases on the early November crust have been observed in the South Columbia Region. Although not widespread in this region, where it exists this layer may be primed for triggering.

Be aware of the potential for full depth avalanches due to a deeply buried crust.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 6

Valid until: Dec 9th, 2012 2:00PM