Avalanche Forecast

Issued: Dec 11th, 2012 9:13AM

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

ccampbell, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Due to limited field observations for the entire period

Weather Forecast

Wednesday: Mostly cloudy with isolated light snowfall bringing 1-3cm of accumulation, freezing levels in valley bottoms, and light northwesterly winds. Thursday: Increasing cloud throughout the day with light snow bringing another 2-5cm, freezing levels remaining in or just above valley bottoms, and winds increasing to strong southwesterlies. Friday: Continued light snow with another 2-5cm, strong southwesterly winds, andÂ freezing levels remaining in or just above valley bottoms.

Avalanche Summary

Reports from throughout the region on Monday include isolated small avalanches with extensive explosives testing. Check out this recent avalanche report from the Kicking Horse backcountry.

Snowpack Summary

Around 80 cm of snow fell over the past week. This loads a surface hoar and/or facet layer that was buried at the end of November. Recent snowpack tests from the Invermere area gave moderate but resistant results on this weakness where it was found as surface hoar down 34cm. A bit deeper (near 100 cm down) another surface hoar layer that developed during mid-November may still be reactive; however, recent testing around the Invermere area has proved this layer to be unreactive. Near the base of the snowpack is the early November crust/facet deep persistent weakness. Recent tests throughout the region suggest that it is primed for triggering if you hit the right spot, with anywhere from easy to hard results but consistent sudden fractures.

Problems

Storm Slabs

Soft surface slabs are expected to develop into wind slabs due to the forecast strong southwesterly winds and new snow.

Be cautious as you transition into wind affected terrain.>Avoid freshly wind loaded features.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

There are two layers of buried surface hoar in the region. Neither have been reactive since the last storm. Professionals are still concerned about these layers in unsupported terrain.

Choose well supported terrain without convexities.>If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Deep Persistent Slabs

Typical trigger points include thin rocky areas on steep unsupported slopes. Step-down avalanches are also a concern.

Avoid convexities or areas with a thin or variable snowpack.>Be aware of thin areas that may propagate to deeper instabilites.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

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