Avalanche Forecast

Issued: Dec 8th, 2012 9:26AM

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

swerner, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Timing of incoming weather is uncertain

Weather Forecast

The Region will be under a cool, windy NW flow through the forecast period. Â Light snow amounts expected, with strong NW winds and freezing levels at valley bottom.Sunday: Mainly dry, snow amounts 5-10 cm, ridgetop winds W 20 km/hr switching NW 30-40 km/hr, alpine temps near -7Monday: Trace of new snow, ridgetop winds NW 30-40 km/hr, alpine temps near -8.Tuesday: Light-moderate snow fall amounts, ridgetop winds SW 20 km/hr, alpine temps near -8.

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 ofÂ 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

Persistent Slabs

Buried surface hoar layers exist in specific locations in the upper metre of the snowpack Rider triggers are likely where this layer sits. Suspect slopes may be sheltered treeline/ below treeline terrain and most reactive in deeper snowpack areas.

Be cautious around open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 5

Wind Slabs

Strong winds and storm snow earlier in the week have been responsible for widespread wind slab development. Although they have most likely gained considerable strength, triggering may still be possible in unsupported terrain.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

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 thin areas that may propagate to deeper instabilites.>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 9th, 2012 2:00PM