Avalanche Forecast

Issued: Mar 18th, 2017 4:48PM

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

cgarritty, Avalanche Canada

Northwest Coastal.

Recent snowfall and winds have been driving a wind slab problem at higher elevations. The potential for a wind slab release to trigger a deeper persistent slab needs to factor into your terrain selection.

Summary

Confidence

Moderate -

Weather Forecast

Sunday: A mix of sun and cloud with isolated flurries and a trace of new snow. Moderate to strong southwest winds. Freezing level to 400 metres with alpine temperatures of around -8.Monday: A mix of sun and cloud. Light east winds. Freezing level to 1000 metres with alpine temperatures of around -4.Tuesday: Cloudy with sunny periods, flurries beginning in the afternoon. Light southeast winds. Freezing level to 1000 metres with alpine temperatures of around -3.

Avalanche Summary

Reports from Thursday include several observations from the north of the region, where skier traffic triggered a Size 2.5 wind slab as well as a Size 2 persistent slab over the late February interface down 50 cm. The large wind slab release was triggered from a thin spot and had a crown fracture that ranged from 30-100 cm. This should draw attention to the significant effect of recent winds as well as the touchy nature of the thin edges of large wind slabs. The bulk of recently reported activity took place on north to northwest aspects.

Snowpack Summary

A steady supply of new snow over Thursday and Friday has been blown into touchy wind slabs by strong southeast to southwest winds at higher elevations. Below the new snow, the previous week of stormy weather delivered approximately 30-60 cm of recent snow, with much deeper areas where the wind transported this snow. At treeline and above, new snow and wind have been loading and stressing a weak interface from February composed of facets, crust, and surface hoar buried over a metre deep. This layer was active prior to the storm and remains an ongoing concern. A non-supportive surface crust has formed over moist or wet snow at 1100 metres and below.

Problems

Wind Slabs

Moderate to strong winds recently shifted from southeast to southwest, leaving fresh wind slabs on a range of aspects. Use increasing caution as you enter wind affected terrain, especially in the lee of exposed terrain features at treeline and above

Be alert to conditions that change with elevation.Use ridges or ribs to avoid pockets of wind loaded snow.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

A persistent weak layer from late February is buried up to a metre deep and continues to show reactivity in snowpack tests. Potential still exists for a rider to directly trigger this layer or for a smaller wind slab avalanche to act as a trigger.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.Avoid steep convexities or areas with a thin or variable snowpack.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Mar 19th, 2017 2:00PM