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Avalanche Forecast

Archived

Jan 12th, 2020–Jan 13th, 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 unlikely, human triggered possible.
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, human triggered possible.

Regions

North Columbia.

Use extra caution around steep and open slopes. A buried weak layer has potential to produce large avalanches at lower elevations, while wind slabs exist at higher elevations.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather. Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

SUNDAY NIGHT: Isolated flurries with up to 5 cm of low density snow, strong wind from the north in the valleys and moderate wind in the alpine, alpine temperatures drop to -25 C.

MONDAY: Mix of sun and cloud, light wind from the west, alpine high temperatures around -22 C.

TUESDAY: Mostly sunny, light wind from the southwest, alpine high temperatures around -25 C.

WEDNESDAY: Sunny, light wind from the southwest, alpine high temperatures around -25 C.

Avalanche Summary

Over the weekend accumulations of low density snow resulted in several small slab and dry loose avalanches (size 1). There have also been ongoing reports of large persistent slab avalanches being reactive to human triggering over the past week. These avalanches have failed on a surface hoar layer roughly 100 cm below the surface and found between elevations of 1200 to 2100 m (and primarily on north and east aspects). Most recently, a large size 3 avalanche on this layer was remotely triggered in the Selkirks on Saturday. Another large persistent slab avalanche was triggered by a snowmobiler in Clemina on Friday (see the photo in this MIN report). The recent pattern of activity suggests this problem remains a serious concern in the North Columbias.

Snowpack Summary

Low density snow continues to accumulate, with 20-40 cm of fresh light snow on the surface. A short lived period of strong northerly wind on Sunday night could transport snow and form wind slabs in unusual places. Otherwise cold temperatures and easing winds should preserve low density snow in most places. A layer of surface hoar is now buried 80-120 cm below the surface and continues to be a concern across the region. A facet/crust layer from late November lingers near the bottom of the snowpack and has occasionally been reactive in isolated shallow snowpack areas.

Terrain and Travel

  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Choose slopes that are well supported and have limited consequence.

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.