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Avalanche Forecast

Archived

Nov 27th, 2017–Nov 28th, 2017

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

Regions

Banff Yoho Kootenay.

There is still much uncertainty with the Oct 31 persistent weak layer. Conservative route choices are still suggested.

Weather Forecast

We are expecting precipitation starting at noon on Tuesday and accumulations of approximately 20cm by end of day Thursday. Luckily, the freezing level is expected to stay below surface and we will see this as snow. Wind will continue in the moderate range from the S-SW.

Snowpack Summary

Continued strong winds have created wind-slabs in lee areas in the alpine and have extended down to some tree line areas. The recent Nov 23 crust is located ~30cm below surface and is producing moderated snowpack test results. The main weakness in the snowpack remains the weak facets associated with the Oct 31 crust now buried ~70cm at treeline.

Avalanche Summary

One audible avalanche was heard by forecasters today near Crowfoot Glades. Likely it came from the cliffs high above. A surprising lack of activity was observed today after last nights warm temperatures and heavy precipitation.

Confidence

Forecast snowfall amounts are uncertain on Thursday

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.

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.