Avalanche Forecast

Issued: Dec 20th, 2015 8:30AM

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.

Extensive wind effect has likely occurred at higher elevations. 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

Light flurries and a mix of sun and cloud are expected for all 3 days of the forecast period. Moderate southwest ridgetop winds forecast for Monday and Tuesday will ease to light and westerly by Wednesday. The freezing level should sit at valley bottom for the foreseeable future. For a more detail weather discussion, please check-out our Mountain Weather Forecast at: avalanche.ca/weather.

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 eventsÂ 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 real concern for a few days.

Snowpack Summary

On Sunday morning there was up to 30cm of fresh snow bringing the 48 hour total to about 50cm in the deeper snowpack parts of the region. Strong southwest winds have redistributed much of this snow into much deeper wind slabs in exposed lee features in the alpine and at treeline. 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 unlikely. 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

Watch for deep and reactive wind slabs on exposed slopes at treeline and in the alpine. The best (and safest) riding may be found in lower elevation sheltered terrain.

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

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

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 21st, 2015 2:00PM