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Avalanche Forecast

Archived

Feb 10th, 2020–Feb 11th, 2020

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

Regions

Little Yoho.

Uncertainty remains around deep persistent slab avalanches and their random occurrences. If they do occur, there is the possibility that they can run to valley floor.

Weather Forecast

Seasonal temperatures are expected for the next few days. Snow will start late tonight and roughly 10cm will accumulate by end of day Tuesday. Alongside the incoming snow will be strong wind from SW.

Snowpack Summary

Up to 20 cm of snow in the past several days. Recent periods of strong wind have created fresh wind slabs at treeline and in the alpine. In many areas a dense mid pack sits over the basal weak layers of facets and depth hoar. Deep snowpack areas (>150 cm) have a denser base. A buried rain crust from February 1st is present up to 1850 m.

Avalanche Summary

A large deep persistent slab avalanche (size 3.5) was observed on the East face of Mt. Lefroy than released on glacier ice today. Additionally, a size 1.5 windslab was observed on Protection Mountain on a SW aspect in the alpine.

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Tuesday

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.