Avalanche Forecast

Issued: Jan 4th, 2014 9:01AM

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

ghelgeson, Avalanche Canada

Purcells.

While humans crave simplicity the current situation is anything but. The answer to the avalanche problem this weekend is staying conservative with terrain selection. Visit the blog for thoughts on the recent pattern of accidents in the Purcells.

Summary

Confidence

Good - Freezing levels are uncertain on Monday

Weather Forecast

A strong, stable northwesterly flow will prevail over the province while a strong upper ridge remains offshore. The mountain top winds should ease Sunday as the upper ridge moves over the coast. The ridge will then weaken somewhat on Monday but will still protect the province from Pacific systems.Sunday: Freezing Level: Valley Bottom; Precip: Nil; Wind: Light, Variable. Strong NW at ridgetop.Monday: Freezing Level: Valley Bottom with chance of an Above Freezing Layer from 1500 2500m. Precip: Nil; Wind: Light Variable, Mod NW at ridgetop.Tuesday: Freezing Level: Valley Bottom; Precip: Trace; Wind: Lht Variable.

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. On Friday avalanches released naturally and with explosive control resulting in avalanches to size 3.5 with crowns up to 2 meters in depth on all aspects.

Snowpack Summary

Thursdays 20 - 40 cm of 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

New snow and fresh wind slabs rest on top of two persistent weak layers in the upper meter of the snowpack. Many slopes are teetering on the edge of failure waiting for a human trigger, particularly exposed lee slopes at and above treeline.

Choose well supported terrain without convexities.>This will take much longer to settle out than your typical storm slab. File the big lines away for another time.>Resist venturing out into complex terrain, even if you observe no obvious signs of unstable snow.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

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.

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 large, deep destructive avalanches.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 6

Valid until: Jan 5th, 2014 2:00PM