Avalanche Forecast

Issued: Mar 21st, 2016 9:28AM

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

Avalanche Canada triley, Avalanche Canada

If the sun comes out on Tuesday, recent storm snow and cornices may release naturally. Cornice falls may trigger deeply buried weak layers resulting in very large avalanches.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

Scattered flurries overnight with light northwest winds and freezing levels down to valley bottoms. On Tuesday, light westerly winds with light precipitation and freezing levels up to 1700 metres during the day with periods of broken skies. On Wednesday, expect 3-5 cm of new snow with moderate southwest winds and a good overnight freeze. Cloudy with freezing levels rising to 1500 metres during the day. On Thursday, continued cloudy with moderate-strong westerly winds and 5-8 cm of new snow.

Avalanche Summary

An early report on Monday of another skier remote triggered avalanche size 2.5 from 200 metres away on a southeast aspect at 2320 metres, believed to have released on the February 27th weak layer. A MIN report from Monday at Gorman lake in the Dogtooth range describes "a lot of cornice failures", as well as "many slides running full path." On Sunday, large cornice releases triggered persistent slabs on slopes below up to size 3.0 in the central part of the region, and a group of skiers remotely triggered a size 2.5 from 6 metres away on a southeast aspect at 2400 metres in the north of the region. On Saturday several natural and explosive initiated cornice failures to size 2.5 were reported. In the north of the region on friday control work produced several size 2 to 3 persistent slab avalanches on high elevation north through east facing features. These avalanches were failing on the mid and early February persistent weak layers.

Snowpack Summary

At ridgetop, cornices are huge and remain weak. Old wind slabs still linger on lee features at treeline and in the alpine which may become more reactive with solar radiation. 40-90cm below the surface you'll find a persistent weak layer comprised of surface hoar, facets and/or a thick crust. This layer seems variably reactive. In other words, it's still reactive to human triggers in some places while in other spots it's really tough to trigger, and there's not much of a reliable pattern telling us what exact aspects are most suspect. I'd continue to be suspicious of steep, unsupported features at treeline and in the alpine as this layer has the potential to produce large avalanches. Deeper weak layers from mid-February and early January are now down 50-90cm and 70-120cm respectively. Triggering an avalanche on either of these layers has become unlikely but still has the potential to produce very large avalanches in isolated locations with a heavy trigger or significant warming.

Problems

Persistent Slabs

An icon showing Persistent Slabs
There have been a few skier remote triggered avalanches from solar aspects in the alpine on this persistent weak layer in the north of the region. This layer continues to be tricky to forecast with respect to distribution and likelihood.
Continue to seek out well supported conservative terrain as you plan your day in the mountains.>Be aware of the potential for large, deep avalanches due to the presence of a few different persistent weak layers.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 6

Cornices

An icon showing Cornices
Cornices may be very large and fragile. Natural cornice falls may trigger deep persistent weak layers resulting in very large avalanches.
Do not travel on slopes that are exposed to cornices overhead.>Cornices become weak with daytime heating. >

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

3 - 5

Storm Slabs

An icon showing Storm Slabs
New storm snow may not be well bonded to the old surface. If the sun comes out, loose wet snow in motion may trigger storm slabs where they are sitting on a crust.
Avoid freshly wind loaded features.>Be alert to conditions that change with elevation.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

Valid until: Mar 22nd, 2016 2:00PM