Avalanche Forecast

Issued: Dec 4th, 2012 9:30AM

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

Avalanche Canada jlammers, Avalanche Canada

Summary

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Overnight and Wednesday: Light to locally moderate snowfall overnight, easing off by late Wednesday / Strong to extreme southwest winds / Freezing level at 1000m dropping to surface by WednesdayThursday: Light snowfall / Moderate west winds / Freezing level at 900mFriday: Possibility of clearing / Light southwest winds / Freezing level at surface

Avalanche Summary

On Monday whumphing and cracking was observed in the Invermere area between 2150m and 1850m. A slab avalanche (50cm deep/ 15-20m wide) was ski cut in the same area on a north aspect between 1900 and 2000m. It was suspected to have run on the early November faceted rain crust. Any field observations can be sent to forecaster@avalanche.ca.

Snowpack Summary

Strong winds and light to locally moderate snowfall are responsible for newly formed wind slabs which are likely to exist at treeline and above. Over the last few days snowfall amounts have been highly variable throughout the region; however, reports indicate that up to 60cm of recent storm snow may sit above a surface hoar layer that was buried on the 28th. Although not widespread in the region, releases on this layer are likely if you have it in your area. A surface hoar layer that developed during mid-november may exist up to 85cm down, but has not been reactive during the recent storm. There is a rain crust near the ground that we're calling the early November crust. There are some facets below it, or it may appear as a sandwich of crusts and facets, but it's been reported as unreactive at this time. There is still a sharp transition in snow depth from treeline to below treeline making back-country travel challenging under 1300 m in elevation.Significant variations in snowpack structure exist across the region. Digging down and making your own observations will be critical to safe slope selection.

Problems

Storm Slabs

An icon showing Storm Slabs
Forecast snowfall and extreme winds will create new wind slabs and potentially add to the reactivity of a storm slab that may sit over weak surface hoar crystals. With expected wind values, loading may occur lower on the slope than normal.
Be aware of the potential for wide propagations due to the presence of hard windslabs.>Be alert to conditions that change with elevation.>

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

An icon showing Persistent Slabs
Two problem layers exist: A surface hoar layer 40 - 85 cm below the snow surface and the early November crust near the ground. It may be possible for a rider to trigger these weak layers, especially in areas where the snowpack is thin and/or rocky.
Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Dec 5th, 2012 2:00PM

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