Avalanche Forecast

Issued: Dec 2nd, 2018 3:00PM

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

jsmith, Avalanche Canada

North Columbia.

There is a lot of uncertainty with the reactivity of the buried surface hoar layer down 40-80 cm. Human triggered avalanches are more likely at treeline and sheltered locations in the alpine where this weak layer may exist. New Forecaster blog HERE.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Overnight SUNDAY: Mostly cloudy / Alpine Low -13 / Light, northwest wind / Freezing level valley bottom.MONDAY: Mix of sun and cloud / Alpine high -12 / Light, northwest wind / Freezing level valley bottom.TUESDAY: Mix of sun and cloud / Alpine high -13 / Moderate, northwest wind / Freezing valley bottom.WEDNESDAY: Sunny / Alpine high -14 / Light, northwest wind / Freezing level valley bottom.

Avalanche Summary

Numerous naturally triggered, loose wet avalanches up to size 1.5 were reported on steep solar aspects on Saturday. We currently have very few observations from within this region. Please post your observations to the Mountain Information Network (MIN). Although not in this region, a notable size 2.5, explosive triggered avalanche was reported south of Revelstoke on Thursday. The avalanche released on the October crust at the bottom of the snowpack in steep, rocky terrain.

Snowpack Summary

There may be some lingering wind slaps in exposed, alpine terrain, but the primary concern in the snowpack is a weak layer of surface hoar (feathery crystals) and/or sun crust depending on the aspect of the terrain. This layer is down 30-70 cm and has been described as 'spotty' with regards to its distribution. It is most pronounced at treeline, but may be found in sheltered, north facing alpine areas.At the base of the snowpack is a crust that formed in late October. There have been no recent reports in this region of reactivity on this layer. However, the South Columbia region has had two large avalanches on this layer, one triggered by a snowmobile and the other a bomb. Steep, rocky terrain, with a shallow snowpack are the most likely areas to trigger this layer.Total snowpack depths vary greatly with elevation. Recent reports show depths of 120-230cm in the alpine, 90-160 cm at treeline and 10-120 cm below treeline. Rocks, stumps, and open creeks remain significant hazards at treeline and below.Check out our latest FORECASTER BLOG for more insight into the uncertainty we have with the surface hoar layer in this region.

Problems

Persistent Slabs

Be especially cautious with this buried weak layer in the Treeline elevation band, on large open slopes that have a deep enough snowpack to bury all the bushes and make the slope smooth. It may also be present in sheltered, N. facing alpine slopes.

Watch for signs of instability such as whumphing, cracking, and evidence of recent avalanches.Use small slopes with no consequence to test for the presence of the buried weak layer.Start in conservative terrain while you gather additional information about the snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 3rd, 2018 2:00PM