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Avalanche Forecast

Archived

Feb 12th, 2017–Feb 13th, 2017

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

Regions

Little Yoho.

Lee areas have been re-loaded by strong winds from the SW creating touchy wind-slabs. Conservative terrain choices will be important to avoid encounters with avalanches over the next few days.

Weather Forecast

The strong/extreme wind from the SW is expected to die down by Monday. A slow warming trend is currently forecast into next week with temperatures reaching close to 0C in the alpine.

Snowpack Summary

40-60 cm of new snow over the past week with extreme SW winds have created new snow slabs over various layers of weaker facets, surface hoar, and buried wind layers. In below treeline areas, this new snow load is sitting on a snowpack entirely made up of facets and depth hoar.

Avalanche Summary

Numerous natural and explosive triggered avalanches were observed and reported throughout the forecast region up to size 3 in the last 72hrs. These have been occurring on many different aspects and at all elevation bands. Most are between 40-60cm in depth, with some "stepping" down to the deeper weak layers.

Confidence

Due to the number and quality of field observations on Sunday

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.

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.