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Avalanche Canada triley, Avalanche Canada

South Rockies Avalanche Forecast

Jan 29th, 2016 8:23AM

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

Touchy wind slabs and avalanches stepping down to the persistent weak layer are the main concerns at this time. Please send your observations to the MIN if you get out in the mountains this weekend.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Light snow combined with strong westerly winds overnight. Freezing levels down to valley bottoms by Saturday morning with 3-5 cm expected. Some clearing during the day on Saturday with moderate to strong west-northwest winds. Scattered cloud and light winds on Sunday with alpine temperatures around -10. Cloudy with light winds and temperatures around -10 at treeline on Monday.

Avalanche Summary

On Friday, our field team reported several size 2.0 natural avalanches on east aspects that were visible from Crown mountain in the Elk Valley North area. These avalanches probably started from wind loading or cornice falls. The interesting observation about these slides was that they stepped down in the track or at the fans around 1800 metres elevation and resulted in a larger avalanche than the initial release. This suggests that it is possible to trigger an avalanche in the run-out with the right load in the wrong place. No new avalanches reported on Thursday. On Wednesday, a natural size 1.5 wind slab released in a cross loaded gulley with a 40cm slab thickness. Explosives also triggered a size 2.5 deep persistent slab avalanche on a south aspect at 2000m in the southeast of the region. This released down 70cm on the early December crust layer. No new avalanches were reported on Tuesday. Wind slabs are expected to remain reactive to human-triggering on Friday at higher elevations.

Snowpack Summary

Recent strong to extreme winds from the south to west have redistributed the snow at treeline and above. Wind slabs have formed on lee slopes and windward slopes are being stripped away. Moist surface snow is being reported up to about treeline elevation on Thursday and a crust is expected to form over the weekend as freezing levels fall. The mid and lower snowpack has been settling well with the warm temperatures and is expected to gain considerable strength with several days of cooling. The buried surface hoar was found in the Crown mountain area, and compression tests gave hard sudden planar results. A weak crust/facet layer from early-December is typically down over 1m. It has become difficult to trigger this layer but it is still reactive in snowpack tests suggesting that if you are able to trigger it, the layer is capable of wide propagations and large destructive avalanches.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Likely

Expected Size

1 - 3
Forecast light snow and continued strong winds may continue to develop new wind slabs and new cornice growth. Avalanches in motion may step down to the deeply buried persistent weak layer.
Avoid freshly wind loaded features. >Be aware of the potential for wide propagations due to the presence of hard windslabs. >Use ridges or ribs to avoid pockets of wind loaded snow. >

Aspects:

North, North East, East, South East.

Elevations:

Alpine, Treeline.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Possible

Expected Size

3 - 5
The persistent weak layer continues to give sudden planar results in snowpack tests in the north of the region. A couple of large natural avalanches in the Lizard-Flathead region suggest that the distribution may be variable.
Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Use extra caution on steep open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Valid until: Jan 30th, 2016 2:00PM