Avalanche Forecast

Issued: Jan 31st, 2017 4:58PM

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

Avalanche Canada jlammers, Avalanche Canada

Be aware of the potential for smaller avalanches to step down to deeper persistent weaknesses. The avalanche danger may be higher in the north of the region where very large, full depth avalanches remain a concern.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Clear skies are expected for Wednesday and Thursday with increased cloud forecast for Friday. Ridgetop winds should remain generally light to moderate from the east for Wednesday and Thursday, intensifying on Friday. Freezing levels should remain at valley bottom for the forecast period.

Avalanche Summary

Over the weekend, alpine and treeline features were observed running naturally to size 3.5 in the mountains northwest of Terrace. A few of these avalanches were thought to have failed on buried surface hoar. Several avalanches involving the full depth of snowpack to size 3.5 were also reported in the Ningunsaw and Bell 2 areas. One was reported being remotely triggered by a skier from a distance of 150m away. Moving forward, natural avalanche activity is expected to taper-off with forecast benign weather; however, large human-triggered persistent and deep persistent avalanches remain a concern.

Snowpack Summary

Last weekend, between 60-110 cm of new snow fell with the greatest amounts accumulating in coastal areas. Strong to extreme southwesterly winds accompanied the storm and much deeper deposits can be found in higher elevation lee terrain. At lower elevations, precipitation fell as rain and a surface (or near-surface) crust may now be found below about 1000m. Below the recent storm snow you'll likely find a couple of buried surface hoar layers from January 18th and January 23rd. These surface hoar layers continue to produce easy to hard sudden planar shears in snowpack tests, and should be approached with caution, especially in sheltered treeline terrain. The snowpack below this is generally strong and well settled. The exceptions are areas around Bear Pass and Ningunsaw where basal facets remain an ongoing concern.

Problems

Persistent Slabs

An icon showing Persistent Slabs
In the mountains closer to Terrace, I'd remain cautious in sheltered treeline terrain where buried surface hoar may be preserved. In the north of the region, full depth avalanches continue to fail on weak layers at the base of the snowpack.
Be aware of thin areas that may propogate to deeper instabilites.Avoid areas with overhead hazard.Be aware of the potential for wide propagations due to the presence of buried surface hoar layers.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 4

Storm Slabs

An icon showing Storm Slabs
Recent storm accumulations have likely gained significant strength. That said, I'd remain cautious in steep, higher elevation lee terrain. Surface avalanches may also step down to deeper, more destructive layers.
Be cautious as you transition into wind affected terrain.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Feb 1st, 2017 2:00PM