Avalanche Forecast

Issued: Jan 7th, 2014 8:20AM

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

mbender, Avalanche Canada

Purcells.

Complex avalanche conditions at the moment. The answer to this type of avalanche problem lies in conservative terrain selection. Visit the blog for thoughts on the recent pattern of accidents in the Purcells.

Summary

Confidence

Good

Weather Forecast

Wednesday: A Pacific frontal system starts to affect the interior regions. Cloudy with light snowfall, moderate to strong west winds. Freezing level in the valley bottom.Thursday: Light snowfall, Alpine temperatures -7, moderate west winds.Friday: Light snowfall, alpine temperatures -5, freezing level 1100m, winds moderate west and southwest

Avalanche Summary

There have been a few different close calls with large avalanches in the north of this region in the last two weeks. Check out the incident database for more details. Recent reports from the last 3 days indicate several natural cornice triggered avalanches running to size 3 on east and southeast aspects at treeline and above. Explosives triggered avalanches have continued to be reported to be running to size 2.5 on northerly aspects in the alpine failing on the October facet/crust layer near the base of the snowpack.

Snowpack Summary

Up to 40 cm of recent storm snow lies on top of old wind slabs and a couple of persistent weak layers that exist in the upper meter of the relatively thin snowpack. The mid December surface hoar is buried around 30-90 cm. The early December facet/crust combo is buried down 50-150 cm. Both interfaces give variable results with snowpack tests, but professional operators are treating them with caution.A bigger concern, especially in the Northern part of the region is a layer of weak sugary depth hoar crystals at the base of the snowpack that lie above a crust from early October. Several large avalanches in the last two weeks have been attributed to failures at this layer. Wide propagations on relatively gentle terrain have been noted, as well as a tendency for seemingly disconnected slopes to become connected by one large avalanche.

Problems

Persistent Slabs

Fresh wind slabs rest on top of two persistent weak layers in the upper meter of the snowpack. Triggering a windslab could add a significant load to the snowpack and possibly step down to a deeper buried persistent weak layer.

Resist venturing out into complex terrain, even if you observe no obvious signs of unstable snow.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Deep Persistent Slabs

You wouldn't build a house with a weak foundation and you can't trust a snowpack with this kind of structural weakness near the ground. You're most likely to trigger this layer on steep north through east facing slopes with a shallow snowpack.

Avoid exposure to slopes with cornices above. A cornice release may be enough load to trigger deeply buried persistent weak layers.>Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Large human triggered avalanches have occurred after riders found stable results from snowpack testing. Large features, especially in the north of the region, should be avoided at this time.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 6

Valid until: Jan 8th, 2014 2:00PM