Avalanche Forecast

Issued: Jan 16th, 2013 9:27AM

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

jlammers, Avalanche Canada

Northwest Inland.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Tonight and Thursday: Light to moderate snowfall Wednesday and Thursday nights / Strong to extreme west winds / Freezing level at 800mFriday: Light snowfall / Moderate west winds /Â Freezing level at 800mSaturday: Dry conditions with overcast skies / Light to moderate west winds / Freezing level at 1200m

Avalanche Summary

On Monday a size 2 windslab avalanche was skier-triggered in a chute above Crater Lake. The crown was about 30m wide with a maximum height of 80cm. On Tuesday a snowmobiler triggered a size 1 windslab on a slope which was reported to be "normally very stable". Reports suggest that the recent strong winds will be responsible for ongoing windslab activity.

Snowpack Summary

On the surface there are signs of recent intense northwest winds in the alpine and at treeline leaving scoured areas and hard windslabs on lee side of ridges and terrain breaks.Â A surface hoar layer that was buried at the end of December is now down 60-80 cm, and has become reactive in some areas with recent warming. An otherwise strong mid-pack overlies a weak base layer of facets/depth hoar and the remnants of a crust.

Problems

Wind Slabs

Strong westerly winds have created windslabs on lee terrain. With forecast snowfall and higher than normal wind values, watch for loading lower on the slope and in other unsuspecting locations.

Be aware of the potential for wide propagations due to the presence of hard windslabs.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Persistent Slabs

Forecast snowfall will add additional load to buried weak layers. Watch for triggering in steeper, unsupported terrain.

Choose well supported terrain without convexities.>Be aware of the potential for large avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 4

Deep Persistent Slabs

A deeply buried facet/crust weakness exists near the base of the snowpack. This layer could be triggered by large loads such as a cornice collapse or from a thin-spot trigger point.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Jan 17th, 2013 2:00PM