Avalanche Forecast

Issued: Jan 20th, 2013 9:48AM

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.

jlammers, Avalanche Canada

Northwest Inland.

Summary

Confidence

Fair - Due to limited field observations

Weather Forecast

The ridge of high pressure will continue to bring dry conditions until Tuesday afternoon at which point the region will see light to moderate snowfall that will continue into Wednesday. Winds are expected to remain generally light from the southwest (moderate in the north). Alpine temperatures are expected to hover around -1.0 on Monday and Tuesday dropping to -6.0 on Wednesday.

Avalanche Summary

On Friday stiff wind slabs were reported to have run naturally in the north of the region on northeast and east aspects. In isolated occurrences, these wind slab avalanches triggered full-depth avalanches that ran on basal facets 100cm below the surface and ran up to 200m wide and 200m long.

Snowpack Summary

A melt freeze crust most likely exists on lower elevation slopes that were previously rain-soaked. Light to locally moderate amounts of recent snow and strong to extreme winds at higher elevations have formed hard wind slabs 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 but is most likely gaining significant strength.An otherwise strong mid-pack overlies a weak base layer of facets/depth hoar and the remnants of a crust.

Problems

Wind Slabs

Strong to extreme westerly winds have created wind slabs on lee terrain. Although they are gaining strength, human triggering remains possible.

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.

Elevations: Alpine, Treeline.

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.>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 21st, 2013 2:00PM