Avalanche Forecast

Archived

Dec 6th, 2019–Dec 7th, 2019

Alpine

Natural and human triggered avalanches likely.

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.

As the snow continues to fall, the weak faceted snowpack has reached threshold in many areas. Avoid exposure to avalanche terrain and allow the snowpack time to adjust (avalanche) to the new load.

Even small sloughs could knock you off an ice climb.

Weather Forecast

The storm continues, bringing another 5-15cm by Saturday night (less snow expected along the Eastern slopes). Winds will peak Saturday morning with gusts up to 60km/hr from the SW, then gradually tapering off as a cooler air system moves in. Expect an alpine high of -8 for Saturday and cooler on Sunday.

Snowpack Summary

40-50cm of new snow has fallen with moderate to strong SW winds, a storm slab is building in the Alpine down to Treeline. Below the storm slab, the snowpack structure is generally weak, consisting of facets and depth hoar. The Nov crust is up to 2400m and ~30cm up from ground. Snowpack depths at treeline are 80-130cm and deeper in lee areas.

Avalanche Summary

Numerous avalanches up to size 2.5 over the last 48 hours as the storm continues. These have been primarily wind/storm slabs in the new snow with isolated avalanches scrubbing deeper into the facets. Explosive control at the local ski areas has produced results up to Sz 2.0 in wind loaded areas.

Poor visibility today limiting observations.

Confidence

Intensity of incoming weather systems is uncertain on Saturday

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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.