Avalanche Forecast

Issued: Apr 9th, 2015 9:18AM

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

bcorrigan, Avalanche Canada

Northwest Coastal.

The danger ratings reflect the hazard in the northern part of the region, for the most part, where the persistent March 25th weakness has been most active. Incoming storms and more snow load may wake up this layer in other parts of the region.

Summary

Confidence

Fair - Due to the number and quality of field observations

Weather Forecast

Increasing clouds with rain or snow at upper elevations starting today, with moderate to locally heavy snow 20-30 cm. Freezing level should be around 1500m for Friday, then fall to 500m overnight and rise to around 1000m on Saturday during the day.. Winds are forecast moderate to strong throughout the forecast period. Precipitation will be heavier towards the coast, but the inland portion of the Northwest Coast may see as much as 45 cm of snowÂ at upper elevations for the period from Thursday to Monday.

Avalanche Summary

For the past few days, there have been reports of natural, skier-triggered, and remotely triggered slabs up to size 2.5 releasing on the March 25th surface hoar layer. Some of these have been triggered from below or in low-angle terrain. In addition, cornices have been failing and loose wet activity has been noted in the afternoon, both of which have triggered deeper persistent slabs.

Snowpack Summary

The snow surface varies from dry faceted powder and/or surface hoar on alpine shaded slopes, to moist snow or a sun crust on sunny slopes. In some places down-flowing winds have created thin wind slabs in lee features lower down the mountainside. Approximately 40-70 cm of snow sits above the March 25th surface hoar layer. This interface seems much touchier in the northern part of the region, but has been reported throughout the northwest coastal area. The early March facet/crust persistent weakness is now down over a metre and produces hard, sudden planar results in snowpack tests.

Problems

Persistent Slabs

The March 25th persistent weak layer should be treated with respect. It could be triggered by a smaller wind slab or a loose wet avalanche, or by a rider in the wrong spot, particularly in the Northern part of the region, or a shallow snow pack area.

Be aware of the potential for large avalanches due to the presence of buried surface hoar.>Choose conservative lines and watch for clues of instability.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Wind Slabs

Winds are expected to increase as the next system approaches. New snow will be redistributed into wind slabs in exposed lee terrain, possibly well below ridge crests

Use ridges or ribs to avoid pockets of wind loaded snow.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Apr 10th, 2015 2:00PM