Avalanche Forecast

Issued: Dec 21st, 2015 8:13AM

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

jlammers, Avalanche Canada

Cariboos.

The wind effect from the last storm seems to be highly variable. The best (and safest) riding may be found on sheltered slopes at treeline and below.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

A fairly benign weather pattern is setting up for the forecast period. Light flurries are expected for Tuesday, but snowfall amounts shouldn't exceed 5cm. Isolated flurries with occasional sunny breaks are forecast for Wedesday and Thursday. Ridgetop winds are forecast to remain mainly light for all 3 days while alpine temperatures should hover between -12 and -15.

Avalanche Summary

On Saturday there was evidence of 2 size 1.5 natural persistent slab avalanches. They failed between 1000 and 1100m, ran for about 100m and were up to 80cm deep. The early December surface hoar interface was the likely culprit in these events I'm sure there has also been a widespread round of natural wind slab activity in response to new snow and wind on Saturday night and Sunday. As the stormy weather eases, I'd expect natural wind slab activity to taper-off; however, human triggering will likely remain a concern for a few days.

Snowpack Summary

Up to about 60cm of new snow fell over the weekend in the deeper snowpack parts of the region. Strong southwest winds redistributed much of this snow into much deeper wind slabs in exposed lee features in the alpine and at treeline. On sheltered lower elevation slopes I expect deep powder and really good riding.Between 80 and 150cm below the surface you'll likely find a weak layer of well-developed surface hoar which was buried in early December. This layer is most widespread and reactive at lower elevations (between 1100m and 1800m.) Snow pit tests suggest that human triggering of this interface has become less likely. That said, if it does fail the overlying slab is stiff enough to propagate over a wide distance. Below this layer, the snowpack is thought to be generally strong and well-settled.

Problems

Wind Slabs

Newly formed wind slabs should strengthen gradually over the next few days. While that happens, I'd stick to lower elevation sheltered slopes where the riding is better (and safer).

The best powder will be found in sheltered locations at or below treeline.>Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

Recent avalanche activity indicates that a layer of surface hoar buried in early December should still be on our radar. Although this layer has become less likely to trigger, I'd be wary of steep roles in cut-blocks and open glades below treeline.

Avoid open slopes, convex rolls, burns, cutblocks and terrain traps when traveling below treeline. >

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Dec 22nd, 2015 2:00PM