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Avalanche Forecast

Archived

Dec 21st, 2018–Dec 22nd, 2018

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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.

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

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.