Avalanche Forecast

Issued: Dec 4th, 2012 9:21AM

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

swerner, Avalanche Canada

Cariboos.

Summary

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

An upper level trough sitting offshore will influence a strong SW, moist onshore flow with a series of embedded systems. As the trailing cold front passes through the interior, freezing levels will fall and snow amounts will be in the light-moderate ranges. Freezing levels will remain near valley bottom for the forecast period.Wednesday: Snow amounts 5-10 cm, ridge top winds W 60km/hr, alpine temps near -11.Thursday: Snow amounts near 10 cm, ridge top winds SW 25 Km/hr, alpine temps near -9.Friday: Snow amounts near 10 cm, ridge top winds S 10 km/hr, and alpine temps near -12.

Avalanche Summary

There are limited recent observations; however, I suspect natural avalanche activity will increase into Wednesday with forecast snowfall and strong winds.

Snowpack Summary

New storm snow 30-50 cm over the past 3 days blankets the region. Instabilities (surface hoar layer, and a thin sun crust) may exist within or down 40-60 cm. We have very limited information on the extent or sensitivity of these layers in this region. A second buried surface hoar layer, down about 115 cm, and the early November rain crust (facet-crust combo), over 140cm down in some locations, remain a concern for isolated deep slab avalanches. Average snow depths at treeline seem to be between 140cm and 180cm. Elevations below 1500m are still reported as below threshold. In general, snowpack data is sparse in this region and significant variations likely exist from one drainage to another. Digging down and making your own observations will be critical to safe slope selection. Any observations from the field are welcome at forecaster@avalanche.ca.

Problems

Wind Slabs

Deep and dense wind slabs are likely in exposed lee slopes and cross-loaded gullies well below ridge crests.

Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Avoid lee and cross-loaded terrain near ridge crests.>

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

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Storm Slabs

Instabilities may exist within or under the recent storm snow (up to 60cm) and may be triggered naturally or by the weight of a person. Expect to find dense wind slabs in exposed north through east facing terrain at all elevations.

Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Persistent Slabs

Although the likelihood of a release is low, the consequences of a persistent slab release could be significant. These layers may wake-up with additional loading.

Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

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