Avalanche Forecast

Issued: Oct 24th, 2012 4:00PM

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

Avalanche Canada jfloyer, Avalanche Canada

Early winter conditions exist. Daily avalanche bulletins start November 20.

Summary

Weather Forecast

Avalanche Summary

The most likely early season problem you’ll have to deal with involves wind and storm slabs that are poorly bonded to the underlying snow. These are most dangerous during and immediately after a storm and are most commonly found in alpine bowls and in the lee of ridgelines. The danger can last much longer where slabs of this season’s snow overlie old patches of snow from last year, on sit on top of glacial ice. This is because the bond between last year’s snow and this year’s is often quite poor. Temperatures will typically fluctuate at this time of year, often bouncing above and below zero C. If you get a rapid spell of warming, or worse—rain, immediately after a good dump of snow, there’s a good chance of seeing an avalanche cycle. The consequences of being caught in an avalanche are heightened at this time of year, since trees, stumps and rocks litter runout zones. This is worth keeping in mind, as getting dragged through this kind of nastiness is definitely something to avoid.

Snowpack Summary

At this time of year, successive early winter storms lead to a rapid buildup of the snowpack. Expect big changes to the snowpack structure with elevation, with full-on winter conditions in the Alpine and little or no coverage lower in the valleys. Here are some things to look for in the snowpack that might help you identify potential avalanche danger. First, the quality of the slab. If the upper slab feels dense and has a tendency to crack or pull apart as a cohesive element, there’s a good chance conditions are primed for a slab avalanche. Second, try to identify areas where you might be riding over old snow from last year. These pockets often exist near the top of bowls, on the shaded side of steep gullies and under cliffs. Basically, they favour steep, high elevation north facing terrain. These pockets cause problems because the new snow from this year often bonds poorly to the old snow surface. This is particularly a problem where the new snow falls on steep glacial ice. Third, if you identify crusts within the snowpack, these can act as sliding layers, as well as promoting the growth of sugary facets above or below.

Problems

Wind Slabs

An icon showing Wind Slabs
Wind slab conditions will develop on lee terrain in exposed areas during storms or when the wind can pick up new snow and blow it around. Feeling dense surface snow and cracking around your skis alert you to this.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 9

Storm Slabs

An icon showing Storm Slabs
Storm slabs are a problem during and immediately following an intense winter storm.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 9

Persistent Slabs

An icon showing Persistent Slabs
The most prevalent (but possibly not the only) persistent weakness at this time of year will be facets that grow next to a crust, or at the interface between old snow/glacial ice from last season and this year’s new snow.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 9

Valid until: Nov 20th, 2012 8:00AM

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