Avalanche Canada kdevine, Avalanche Canada

South Rockies Avalanche Forecast

Dec 20th, 2018 4:55PM

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

The storm and associated natural avalanches have tapered off, but the snowpack remains generally weak. Any avalanche triggered within the storm snow is likely to step down to the base of the snowpack, resulting in full depth avalanches.

Summary

Confidence

Moderate - Due to the number of field observations.

Weather Forecast

THURSDAY NIGHT: Mainly cloudy with scattered flurries, up to 5 cm, southwest winds, 60-80 km/h, alpine low temperature near -5°c, freezing level 2000m. FRIDAY: A mix of sun and cloud, west winds, 50-60 km/h, alpine high temperature near -8°c, freezing level 1200m and dropping to valley bottom by the evening. SATURDAY: Sunny with cloudy periods, southwest winds, 20-40 km/h, alpine high temperature near -12°c, low temperature near -14°c. SUNDAY: Cloudy with sunny periods and isolated flurries, southwest winds, 50-70 km/h, alpine high temperature near -8°c, low temperature near -10°c.

Avalanche Summary

One size 1.5 explosives triggered avalanche was reported on Thursday. No new natural avalanches were reported in the region. Several explosives triggered size 2 avalanches on northeast aspects at 2200-2300 m were reported in the region on Wednesday. Widespread natural avalanche activity was observed around Elkford and Sparwood on Tuesday during the height of the storm. Snowmobiles remotely triggered several small avalanches below treeline on cutbanks north of Sparwood on Tuesday. Although these avalanches were small, they involved the entire depth of the snowpack and failed on weak layers at the base of the snowpack. See this MIN report.

Snowpack Summary

30-70 cm of recent snow is sitting on a weak layer of facets (sugary snow) that formed during the dry weather in early December. Wind and warm temperatures have promoted widespread storm slab formation over this layer. The lower snowpack has a weak structure composed primarily of facets. It is likely that an avalanche triggered in the storm snow, would entrain the facets at the base of the snowpack, resulting in a full depth avalanche.

Problems

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

Likelihood

Possible

Expected Size

1.5 - 2.5
Any avalanche in the upper snowpack will likely step down to the weak snow at the bottom of the snowpack and produce large full depth avalanches.
Use conservative route selection, choose moderate angled and supported terrain with low consequence.Back off if you encounter signs of instability like whumphing, shooting cracks or recent avalanches.Minimize overhead exposure; avalanches may reach the end of run out zones.

Aspects:

All aspects.

Elevations:

All elevations.

Storm Slabs

An icon showing Storm Slabs

Likelihood

Possible

Expected Size

1 - 2
Approximately 65 cm of snow sits on a weak layer of facets (sugary snow).
Avoid freshly wind loaded features.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Dec 21st, 2018 2:00PM