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Avalanche Forecast

Archived

Jan 26th, 2020–Jan 27th, 2020

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

Regions

Little Yoho.

Two problem snowpack layers vary a great deal throughout the forecast region. Although natural avalanche activity has tapered, human triggering is still considered quite possible. Make conservative terrain choices and investigate the snowpack closely

Weather Forecast

Moderate to strong winds are expected to continue Sunday night as a cold front passes the area bringing trace amounts of snow. As a second frontal system crosses the divide Monday, winds are expected to remain elevated. Light precip will continue Monday amounts may increase on Tuesday but will favor the West side of the divide.

Snowpack Summary

Recent wind slabs can be found near ridge-tops. There is 40-60 cm above the Dec 31 layer of facets, surface hoar and sun crust which produces variable test results through the region. The bottom layer of the snow-pack consists of weak facets and depth hoar, except for in deeper snow-pack areas (over 2m) where the basal facets are not as prominent.

Avalanche Summary

A large natural avalanche over Cascade waterfall occurred Friday failing on the basal facets/depth hoar (possibly triggered by warm temperatures and solar input). Past 72hrs: a wind slab stepped down to the persistent layer on Mt Bourgeau- sz 2.5, and two explosive triggered avalanches stepped down to basal layers on the north side of Whitehorn.

Confidence

Intensity of incoming weather systems is uncertain on Tuesday

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.

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.