Avalanche Forecast

Issued: Mar 20th, 2017 4:55PM

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.

Avalanche Canada cgarritty, Avalanche Canada

Recent snowfall and shifting winds have been driving a wind slab problem at higher elevations. The same winds have created touchy cornices.

Summary

Confidence

Moderate -

Weather Forecast

Tuesday: Mainly cloudy with scattered flurries bringing approximately 5 cm of new snow, beginning in the afternoon. Light to moderate east winds. Freezing level to 900 metres with alpine temperatures around -3.Wednesday: Cloudy with flurries bringing approximately 10 cm of new snow over the day. Light to moderate south winds. Freezing level to 800 metres with alpine temperatures around -4.Thursday: Continuing flurries bringing approximately 5 cm of new snow over the day. Light to moderate south winds. Freezing level to 900 metres with alpine temperatures around -3.

Avalanche Summary

A social media report from Sunday described very touchy cornices in the Wolf's Den area north of Terrace, with remote triggering occurring from as far away as 25 metres. A social media/MIN report from the Exstew area shows a recent Size 3 avalanche that appears to have triggered naturally and quite possibly over the late February weak layer.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 activity took place on north to northwest aspects.

Snowpack Summary

Clear skies have formed sun crust at the surface on solar aspects over much of the region. Below the surface, last week's stormy weather delivered approximately 40-70 cm of new snow over the week. Winds since the storm have been shifting between southeast and southwest, redistributing this snow into touchy wind slabs on a range of aspects at higher elevations. Recent observations have described a touchy rain crust layer buried approximately 40 cm deep within the storm snow. At treeline and above, new snowfall and wind loading have been stressing a weak interface from late February composed of facets, crust, and surface hoar buried over a metre deep. Recent reports suggest that this layer may remain active in the south of the region. It is substantially more 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

An icon showing Wind Slabs
Recent winds have been shifting between a variety of directions and have formed reactive wind slabs on a wide range of aspects. Be aware that the same winds have also been building touchy cornices that have recently released with remote triggers.
Be alert to conditions that change with elevation.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be aware of especially touchy conditions where slabs overlie a recent rain crust layer.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

An icon showing 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 or cornice to act as a trigger
Be aware of the potential for large 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 21st, 2017 2:00PM

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