Avalanche Forecast

Issued: Dec 21st, 2018 4:43PM

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

kdevine, Avalanche Canada

South Rockies.

Avalanche activity has slowed down, but the snowpack remains generally weak. Choose conservative terrain and pay close attention to signs of instability such as whumphing and cracking in the snow.

Summary

Confidence

Moderate - Due to the number of field observations.

Weather Forecast

FRIDAY NIGHT - Clear periods, west winds, 30-40 km/h, alpine low temperature near -14°c. SATURDAY - A mix of sun and cloud, west to southwest winds, 15-30 km/h, alpine high temperature near -9°c. SUNDAY - Cloudy with sunny periods, southwest winds, 20-40 km/h, alpine high temperature near -8°c, low temperature near -10°c. MONDAY - Cloudy with sunny periods and isolated flurries / light west to northwest winds / alpine high temperature near -7°c, low temperature near -10°c.

Avalanche Summary

One natural size 2 avalanche that was triggered by a cornice was reported in the region on Friday. 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

60-90 cm of recent snow has formed widespread storm slabs that are sitting on a weak layer of facets (sugary snow) that formed during the dry weather in early December. Avalanche activity on this layer has slowed down, but in certain terrain features, it is likely that it would still be easy for humans to trigger avalanches on this layer. Features where the underlying ground surface is smooth, and areas where the snowpack varies from thin to thick would be the most likely places for humans to trigger an avalanche on 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

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.

Back off if you encounter signs of instability like whumphing, shooting cracks or recent avalanches.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Storm Slabs

65-75 cm of snow sits on a weak layer of facets (sugary snow).

If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Avoid freshly wind loaded features.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 22nd, 2018 2:00PM