Avalanche Forecast

Issued: Dec 9th, 2012 9:24AM

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.

triley, Avalanche Canada

Purcells.

I may be a little High on my Danger Rating for the Alpine if the forecast strong gusty NW winds don't show up during the day.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Tuesday

Weather Forecast

Overnight and Monday: Light precipitation and moderate Westerly winds overnight are expected to shift to the NW during the day and become gusty up to 60 km/hr. Freezing level should be about valley bottom, and alpine temperature about -7.0TuesdayWinds SW 30 km/hr becoming NW 30 and gusting to 50 km/hr. Freezing level rising up to 900 metres bringing 5-10 cms of snow to most elevations. Alpine temperatures about -7.0.Wednesday:There should be a bit of a dry spell during the day with light NE winds. Alpine temperatures near -13.0

Avalanche Summary

No new avalanche activity reported.

Snowpack Summary

Wind slabs exist in the upper snowpack on north to northeast aspects at treeline and above. Last weeks storm snow and moderate winds have also shaped unseasonably large cornices. Around 80 cm of snow fell over the past week. This loads a surface hoar layer that was buried on November 28th. Although not widespread in the region, releases on this layer may be likely if you have it in your area. A bit deeper (near 100 cm down) another surface hoar layer that developed during mid-November may still exist. Recent testing around the Invermere area has proved this layer to be unreactive. This does not mean its unreactive throughout the region. Its important to dig down in your local riding area, and test these layers before you disregard them. Near the base of the snowpack is the early November crust. Facet sit facets below it, or it may appear as a sandwich of crusts and facets. In some areas it may only now be primed for triggering with recent heavy loading. Observations have been limited; however, deep and destructive slides have been reported on this layer in a neighboring region.

Problems

Storm Slabs

Some soft storm slabs have developed from the recent snow. Loose snow sluffing in steep terrain on most aspects. Watch for overnight winds starting to stiffen into wind slabs.

The new snow will require several days to settle and stabilize.>Avoid freshly wind loaded features.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

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.

Avoid open slopes and convex rolls where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Deep Persistent Slabs

Recent heavy loading in some areas mean that deep persistent slabs may be primed for triggering. Deep and destructive slides have been reported on this layer in a neighboring region.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely

Expected Size

3 - 6

Valid until: Dec 10th, 2012 2:00PM