Avalanche Forecast

Issued: Dec 6th, 2012 9:57AM

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

jlammers, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Overnight and Friday: Light snowfall (w/ locally moderate accumulations) / moderate west winds with strong gusts / Freezing level at 900mSaturday: No precipitation / Light northwest winds / Freezing level at surfaceSunday: Light snowfall / Light southwest winds / Freezing level at 400m

Avalanche Summary

On Wednesday several natural avalanches to size 2 were reported from the region while explosives control produced isolated releases to size 2.5. These releases which occurred at treeline and above are suspected to have run within recent storm/wind layers or on the late November surface hoar. No avalanches were reported from the region on Thursday.

Snowpack Summary

Recent snowfall amounts have been highly variable, but in deeper areas up to 85 cm of settled storm snow has fallen in the past week. This snowfall was accompanied by generally moderate to more recently strong and variable winds, forming deep and reactive wind slabs in exposed leeward terrain. Below the recent storm snow is a layer of surface hoar that was buried at the end of November. This layer continues to be reactive. At the base of the snowpack sits the early November rain crust. This layer seems most likely to be found in deeper snowpack areas at higher elevations. I'm not aware of any activity on this layer in the Kootenay Boundary region; however, deep and destructive releases have been observed in the South Columbia region (directly to the north). This indicates to me that, where it exists, this layer may now be primed for triggering.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. Any observations from the field are welcome at forecaster@avalanche.ca.

Problems

Persistent Slabs

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

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 5

Wind Slabs

In some areas continuous snowfall and wind has created an ongoing wind/storm slab problem. Watch for triggering in gullies, below ridge crests and behind terrain features.

Be cautious as you transition into wind affected terrain.>

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Deep Persistent Slabs

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

Avoid exposure to overhead avalanche terrain, as large avalanches may reach the end of runout zones.>Be aware of the potential for full depth avalanches due to deeply buried weak layers.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 6

Valid until: Dec 7th, 2012 2:00PM