Avalanche Forecast

Issued: Jan 8th, 2014 8:16AM

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

Fair - Timing, track, or intensity of incoming weather system is uncertain on Friday

Weather Forecast

A westerly flow dominates the next 3 days. A number of weather systems are lined up to bring varying amounts of precipitation and wind to the interior regions.Thursday: Light snowfall, Alpine temperatures -7, moderate west winds.Friday: Light snowfall, alpine temperatures -5, winds moderate west and southwestSaturday: Light snowfall in the northern portion of the region. Moderate to locally heavy snowfall for the mid to southern portions of the region. Alpine temperatures -5, freezing level up to 1300m, winds moderate to strong west.

Avalanche Summary

There have been a few different close calls with large avalanches in the north of this region in the last three weeks. Check out the incident database for more details. Recent reports from the last 4 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 5 cm of new snow sits on a variety of snow surfaces ranging from stiff wind slab, a soft layer of facetted snow and/or surface hoar. These sit 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

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

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Deep Persistent Slabs

You would not 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.

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.>Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Avoid exposure to slopes with cornices above. A cornice release may be enough load to trigger deeply buried persistent weak layers.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 6

Valid until: Jan 9th, 2014 2:00PM