Avalanche Forecast

Issued: Dec 11th, 2012 9:22AM

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

ccampbell, Avalanche Canada

Kootenay Boundary.

Summary

Confidence

Fair - Due to limited field observations for the entire period

Weather Forecast

Wednesday: Mostly cloudy with light snowfall bringing 2-5cm of accumulation, freezing levels around 500m, and light northwesterly winds. Thursday: Mostly clear in the morning with increasing cloud throughout the day and snow starting in the evening, freezing levels rising as high as 500m, and winds increasing to moderate southwesterlies. Friday: Snow easing throughout the day with 5-15cm total since Thursday, moderate southwesterly winds and freezing levels hovering around 500m.

Avalanche Summary

Reports from Monday are limited to relatively harmless surface sluffing with ski cuts. Recent explosive control work triggered several 1.5-2.0 slab avalanches on SE-SW aspects 1700 m and above. These avalanches failed on a rain crust that got buried at the beginning of December.

Snowpack Summary

Weakness exist within and under recent storm snow. Most notably is surface hoar that recently gave moderate to hard but sudden results in compression tests where it has been found as large as 10mm in size down 75-100cm. Elsewhere, are facets sitting on a rain crust that recently gave moderate but resistant compression test results where they were found down 30-35cm on a southwest aspect at 2020m in a shallow area of Kootenay Pass. 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. Recent reports suggest that this deep persistent weakness has been producing inconsistent, but occasionally sudden snowpack test results and remains a concern. 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. Finally, expect to find significant variations in snowpack structure from one drainage to another, so digging down and making your own observations may be critical to safe slope selection.

Problems

Storm Slabs

There is a soft slab on the surface that is stiffening with with continued settlement and wind-exposure. These slabs may be triggered by light additional loads like a skier or rider.

Avoid freshly wind loaded features.>Be cautious as you transition into wind affected terrain.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>On steep slopes, pull over periodically or cut into a new line to manage sluffing.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

The buried surface hoar layer from late November may become reactive from the additional load of new snow and wind transported snow.

Choose well supported terrain without convexities.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Valid until: Dec 12th, 2012 2:00PM