Avalanche Forecast

Issued: Jan 17th, 2013 9:52AM

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 - Intensity of incoming weather is uncertain

Weather Forecast

Overnight Thursday and Friday: Moderate snowfall becoming light on Friday / Strong to extreme southwest winds becoming moderate and northwesterly / Alpine temperatures at about -4.0Saturday: Light snowfall / Moderate west winds /Â Alpine temperatures at about -2.0Sunday: Mainly dry conditions / Light southwest winds / Alpine temperature of about -1.0

Avalanche Summary

Due to inclement weather, observations have been limited; however, 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". Forecast weather suggests that there will be ongoing windslab activity.

Snowpack Summary

Rain below treeline has continued to maintain moist surfaces at lower elevations. Moderate amounts of new snow and strong winds at higher elevations have most likely formed hard windslabs in the lee of terrain breaks and ridges.A surface hoar layer that was buried at the end of December is now down 60-80 cm, and was 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 continued 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 sheltered, unsupported terrain.

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

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.

Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Jan 18th, 2013 2:00PM