Avalanche Forecast

Issued: Dec 13th, 2012 9:25AM

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

pgoddard, Avalanche Canada

Northwest Inland.

Summary

Confidence

Fair - Timing of incoming weather is uncertain for the entire period

Weather Forecast

Friday: Strong W to SW winds. Alpine temp -5. Light snow starting late in the day.Saturday: Strong to gale SW winds. Alpine temp -6. Moderate to heavy snow. Sunday: Light SE winds. Alpine temp -13. Light snow.

Avalanche Summary

On Wednesday, a snowmobile triggered a hard wind slab at the Sinclair snowmobiling area. It failed on the November crust/facet layer 30 cm above the ground. Evidence of a recent natural cycle was also reported. This deep crust/facet layer has been the failure plane for a number of large avalanches further to the west and was suspected to have failed at the Hankin-Evelyn area last weekend. Unfortunately, this weakness is unlikely to heal very quickly, so further deep avalanches are possible, especially as snow and wind-loading continue to stress the snowpack over the next few days.

Snowpack Summary

Storm snow instabilities are likely to continue developing over the next few days as variable new snow layers build up. Spotty surface hoar is also buried in the upper snowpack, particularly in sheltered treeline areas. New and buried wind slabs are widespread and exist on a variety of alpine and exposed treeline slopes due to variable winds. Of key concern is a November facet/crust layer which can be found near the base of the snowpack. This layer, which is widespread, can be triggered from thin-spot trigger points, or with a heavy load, such as storm slabs stepping down, cornice fall or a snowmobile. It has the potential for very large, destructive avalanches and demands respect. A rain crust is buried in the upper snowpack at low elevations. In general the snowpack is highly variable in depth due to windy conditions this season.

Problems

Storm Slabs

Storm slabs are likely to be encountered on many slopes. Be alert for new and buried wind slabs behind ridges and ribs. Storm/wind slabs could step down to trigger a persistent weakness, creating a very large avalanche.

Highmark or enter your line well below ridge crests to avoid wind loaded pillows.>Be aware of thin areas that may propagate to deeper instabilites.>Use ridges or ribs to avoid pockets of wind loaded snow.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 5

Deep Persistent Slabs

A deeply buried facet/crust weakness exists. Very large and destructive avalanches may be triggered from thin snowpack areas or by heavy loads such as a storm slab stepping down, or a snowmobile spinning its tracks.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Avoid shallow snowpack areas where triggering is more likely.>Avoid steep slopes below cornices.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 6

Valid until: Dec 14th, 2012 2:00PM