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Avalanche Forecast

Archived

Jan 29th, 2017–Jan 30th, 2017

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

Regions

Cariboos.

Thin new wind slabs are expected to be touchy on Monday. Use extra caution in wind exposed terrain and watch for signs of recent wind loading.Persistent slab avalanches remain a serious concern and conservative terrain selection is very important.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

5-15 cm of new snow is expected Sunday night before an Arctic front moves southwards on Monday bringing a return to cold and dry conditions which is expected to persist for several days. A mix of sun and cloud is expected on Monday with treeline temperatures around -10C and the possibility of lingering flurries in the morning. Alpine wind is forecast to be moderate to strong from northwest in the morning and ease off in the afternoon. Mostly sunny conditions are forecast for Tuesday and Wednesday with light alpine wind from the northeast and treeline temperatures around -15C.

Avalanche Summary

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 Monday, ongoing moderate to strong wind with small amounts of new snow from Sunday night is expected to continue to develop touchy new wind slabs. Recent wind has been from variety of aspects and wind slabs should be expected on all aspects. 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

50-70 cm of old snow has settled over the mid-January interface which 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. Ongoing moderate to strong winds in exposed terrain have been forming new wind slabs over the weekend. The new snow and strong winds on Sunday night are expected to add additional load to these touchy wind slabs. 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 this sensitivity is expected to continue 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.