Avalanche Forecast

Issued: Mar 19th, 2017 3:09PM

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 shifting winds have been driving a wind slab problem at higher elevations. Slabs have proven especially touchy where they overlie a recent rain crust.

Summary

Confidence

Moderate -

Weather Forecast

Monday: A mix of sun and cloud. Light east winds. Freezing level to 1000 metres with alpine temperatures of -4.Tuesday: Cloudy with sunny periods and flurries beginning in the evening. Light southeast winds. Freezing level to 1000 metres with alpine temperatures of -3.Wednesday: Cloudy with scattered flurries bringing 5-10 cm of new snow. Strong southeast winds. Freezing level to 1000 metres with alpine temperatures of -2.

Avalanche Summary

Reports from Saturday included observations of the evidence of several recent natural Size 2 storm slab releases that occurred at 1300-1400 metres. One natural Size 2 was also directly observed running from a steep unskiable terrain feature as direct result of ongoing wind loading. The above activity took place mainly on north to east aspects, highlighting the recent change in wind direction.A report from Thursday included 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. This activity took place on north to northwest aspects.

Snowpack Summary

Last week's stormy weather delivered approximately 40-70 cm of new snow over the week. Strong southeast and more recent southwest winds have been redistributing this snow into touchy wind slabs on a range of aspects at higher elevations. At treeline and above, new snowfall and wind loading have been stressing a weak interface from February composed of facets, crust, and surface hoar buried over a metre deep. This layer has seen a recent decline in reactivity in the south of the region but remains an ongoing concern. It remains quite active and presents a more serious concern in the north of the region. A non-supportive surface crust has formed over moist or wet snow at 1100 metres and below.

Problems

Wind Slabs

Recent winds have been shifting between a variety of directions and are set to do so again on Monday. Expect to find wind slabs on a range of aspects as you gain elevation and be aware of a recently formed rain crust acting as a touchy sliding layer.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

A persistent weak layer from late February is buried over a metre deep and it needs more time to fully heal into the snowpack. Potential still exists for a rider to directly trigger this layer or for a smaller wind slab avalanche to act as a trigger.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Mar 20th, 2017 2:00PM