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Avalanche Forecast

Archived

Dec 8th, 2019–Dec 9th, 2019

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

Regions

Little Yoho.

The Nov crust/facet layer is becoming reactive and was the sliding layer in several large avalanches across the forecast region today. Although natural activity has tapered, human triggering remains real.

Weather Forecast

Continued NW wind in the moderate range is expected overnight. Temperatures should remain seasonal in the -10 range. Minimal snow and mixes of sun and cloudy periods for the next few days.

Snowpack Summary

40-60+ cm of snow has fallen in the last 4 days. A storm slab has formed at treeline and above. Below the storm slab, the snowpack structure is generally weak, consisting of facets and depth hoar. The Nov crust exists up to 2500m and 30 cm up from ground. Snowpack depths at treeline are 80-130 cm and deeper in lee areas.

Avalanche Summary

A skier accidental size 2.5 was reported in West Bowl at Lake Louise today. The snowboarder was able to ride off to the side. This avalanche slid on the Nov crust layer. Sunshine Patrol also reported some very large explosive controlled avalanches in the Delirium Dive today up to size 3. These slides also ran on the Nov layer.

Confidence

Due to the number and quality of field observations on Sunday

Problems

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.

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.