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Avalanche Forecast

Archived

Jan 27th, 2020–Jan 28th, 2020

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.
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.

With significant winds transporting snow to form wind slabs in the alpine, the likelihood of triggering serious slabs on the persistent and deep persistent layers is on the rise.

Weather Forecast

Light snowfall is expected Tuesday however amounts will favor the West side of the divide. Watch for winds to peak at strong in the alpine. Snowfall for Wednesday will be lighter however watch for alpine winds to reach extreme. By the end of the day Thursday, a significant system is expected to reach the forecast region.

Snowpack Summary

Recent wind slabs can be found near ridge-tops. There is 40-80 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 . A size 2.5 Na was observed today on the S side on Mt Lipalian that looks 40-60 deep likely indicating a failure on the Dec 31 persistent layer. The forecasting trip to Takakkaw falls area saw few small wind slabs in the alpine.

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.