Avalanche Forecast

Issued: Dec 17th, 2012 9:16AM

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

jfloyer, Avalanche Canada

Northwest Inland.

Summary

Confidence

Fair - Due to limited field observations

Weather Forecast

Tuesday: Expect flurries with some clearer spells, treeline temperatures around -12C and light SW winds that may pick up in the afternoon.Wednesday: A Pacific frontal system makes landfall overnight Tuesday/Wednesday bringing 5-10 cm new snow to this region. At the onset of the storm, winds will blow up to 60 km/h from the SW, then reduce in strength to around 30 km/h from the south through most of Wednesday. Treeline temperatures should be around -7C.Thursday: The tail end of the storm will bring further light snowfall (less than 5 cm expected), moderate SE'ly winds and treeline temperatures around -10C.

Avalanche Summary

No recent avalanches have been reported. On Wednesday last week, 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 while side hilling. 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.

Snowpack Summary

Storm snow instabilities are likely slowly settling and gaining strength. Spotty surface hoar was buried in the upper snowpack on Saturday, 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, a cornice fall or a snowmobile track digging a trench. It has the potential for large, destructive avalanches. . In general the snowpack depths, and therefore strength is highly variable due to windy conditions this season.

Problems

Wind Slabs

Storm slabs might be encountered on steeper slopes with recent new snow. The bigger issue is linked to the wind. Be alert for new and buried wind slabs behind ridges and ribs.

Be cautious as you transition into wind affected terrain.>Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Deep Persistent Slabs

A deeply buried facet/crust weakness exists. This layer could be triggered by large loads, such as a cornice collapse or a rider digging deeply with a spinning track in a shallow spot on a steep, slope.

Carefully evaluate and use caution around thin snowpack areas.>Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Carefully evaluate big terrain features by digging and testing on adjacent, safe slopes.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 6

Valid until: Dec 18th, 2012 2:00PM