Avalanche Forecast

Issued: Mar 15th, 2012 10:32AM

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

Avalanche Canada triley, Avalanche Canada

Expect natural avalanche activity if there are few clouds and the sun starts baking the storm slab.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Friday

Weather Forecast

Strong southerly winds combined with moderate snowfall are expected to continue until around midnight. The wind should clock to the west and lighten by morning as mostly clear skies show the sun for a couple of hours. Cloud and convective flurries with light southwest wind are forecast for the afternoon as the freezing level rises to about 900 metres. More cloud is expected to move in from the southwest in the morning on Saturday. The North Columbia may have scattered cloud until the afternoon when it is forecast to become overcast. The South Columbia and Purcell should cloud over by early morning. The south and west of the region could see up to 15cm and the north and east may get 5-10 cm on Saturday. Sunday may be mostly clear with only scattered clouds and light winds. Periods of strong solar radiation are possible.

Avalanche Summary

Avalanches continue to be reported from various aspects and all elevations. Large avalanches are reported from explosive control work in the west and north of the region where the snowpack is a bit deeper. A skier remotely triggered a size 3.0 avalanche from about 50 metres away on Wednesday in Canyon Creek. The slide was reported to be from a west aspect below treeline at about 2000 metres. Expect natural and easily triggered avalanches to continue. If the sun comes out, expect natural activity in the storm slab that may step down to the PWL once it is in motion.

Snowpack Summary

Another 10 cm on Thursday, 80-160 cm storm snow now overlies the prominent surface hoar layer of mid-February. There is 55 cm of foot penetration, which means that there is a lot of snow available for transport by the wind. The storm snow is reacting readily to both natural and human triggers. The mid-February surface hoar layer is more stubborn and not reacting everywhere, but has regularly been producing large avalanches up to size 3.5, which indicates it is very much still alive and needs to be treated with the utmost respect. This layer is widespread, so defining safe zones based on elevation or aspect may not be the best idea right now. Of course, shallower snowpack areas are those where you are more likely to trigger it, as well as convex rolls, and rocky or uneven terrain features. If you know that a slope has already avalanched on that layer, it may be a better bet, although you still need to factor in the effect of recent storm snow amounts and whether reloading is an issue. Operators continue to monitor basal facets, especially in shallow, rocky areas, but with all the recent storm snow, the basal weakness has not been of undue concern recently.

Problems

Wind Slabs

An icon showing Wind Slabs
Mostly S and SW winds, however, recent reverse-loading has occurred in response to E winds. Expect wind slabs to be fat, touchy and widespread.

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

Elevations: Alpine, Treeline.

Likelihood

Very Likely - Certain

Expected Size

2 - 6

Persistent Slabs

An icon showing Persistent Slabs
The deep nature of the mid-February surface hoar layer makes potential avalanches triggered on this layer large and destructive. Regular and ongoing avalanche activity associated with this layer indicates it is very much still alive.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

4 - 8

Storm Slabs

An icon showing Storm Slabs
Storm slabs continue to build and consolidate. The dense storm slab may be easily triggered by light additional loads. Solar radiation may trigger another round of natural activity.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

2 - 6

Valid until: Mar 16th, 2012 9:00AM

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