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Avalanche Forecast

Archived

Jan 30th, 2017–Jan 31st, 2017

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

Regions

Cariboos.

Recently formed wind slabs are the main concern for most of the region. In places that saw more than 30 cm of new snow, a more widespread storm slab problem may exist. Persistent slab avalanches also remain a serious concern for the region.

Confidence

Moderate -

Weather Forecast

A ridge of high of pressure is forecast to keep the region cold and dry for the next several days. On Tuesday, a mix of sun and cloud is expected with light to moderate northeast wind in the alpine and treeline temperatures around -15C. Wednesday and Thursday are forecast to be sunny with light northeast wind in the alpine and treeline temperatures remaining around -15C.

Avalanche Summary

On Sunday, a skier triggered a size 1 wind slab north of Wells Grey on a northeast aspect which was 5-15 cm thick. On Saturday, a natural size 3 avalanche was reported west of Valemount on a northeast aspect at 2400 m elevation. A MIN report from Saturday describes a large avalanche west of McBride. Click here for more details. On Tuesday, recently formed wind slabs are expected to remain reactive to human triggering. Winds have recently switched from south to north and wind slabs should be expected on all aspects.  In the north of the region where more than 30 cm of new snow accumulated, a more widespread storm slab problem may have developed. Persistent slab avalanches also remain a serious concern for the region. Last week there were numerous large human triggered avalanches and several of these avalanches involved multiple people being buried. These avalanches all released on or stepped down to the mid-December weak layer down 1-1.5 m in the snowpack. Check out the MIN posts for more details and photos of these large, human triggered avalanches. Click here for an example of a persistent slab avalanche that was triggered in fairly mellow terrain.

Snowpack Summary

Recent strong shifting winds have redistributed the new snow and formed wind slabs on a variety of aspects in wind exposed terrain. In the north of the region which received more recent snowfall, a more widespread storm slab may have developed.  The mid-January interface is now down 50-70 cm and consists of buried surface hoar in sheltered areas, old wind slabs in exposed terrain, and/or widespread faceted old snow. The interface has generally stabilized but isolated weaknesses may still exist where buried surface hoar is preserved. The mid-December surface hoar/facet weakness is now found down 50 cm in shallow snowpack areas, or as much as 1.5 m in deeper snowpack areas. This layer woke up during the last storm and has remained reactive to human triggers. This weak layer is responsible for several large human-triggered avalanches, including some with multiple burials, and the layer may continue to remain reactive for the foreseeable future.For more information, check out this video of our field team testing the snowpack near Barkerville: https://vimeo.com/201318688 or click here.

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.