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Avalanche Forecast

Archived

Jan 9th, 2021–Jan 10th, 2021

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

Regions

Northwest Inland.

  

Extreme southerly winds will form fresh wind slabs on lee features at treeline and above. Avoid freshly wind loaded features, especially near ridge crests, roll-overs, and in steep terrain. 

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

  

SATURDAY NIGHT: Cloudy with isolated flurries; 0-3 cm. / Extreme, south ridgetop wind / alpine low temperature -11 / Freezing level valley bottom.

SUNDAY: Flurries; 3-5 cm. / Extreme, south ridgetop wind / alpine high temperature -6 / Freezing level valley bottom.

MONDAY: Flurries; 3-5 cm. / Strong, southwest ridgetop wind / alpine high temperature -4 / Freezing level 700 m.

TUESDAY: Flurries; 3-5 cm. / Extreme, south ridgetop wind / alpine high temperature -4 / Freezing level 700 m.

Avalanche Summary

Avalanche activity is beginning to slow down. However, previous to Thursday, there had been steady reports of natural wind slab avalanches in alpine terrain (size 1-2), and some smaller human-triggered wind slab avalanches in lee terrain (size 1). There are good photos of these avalanches in recent MIN reports (e.g. here, here, here, and here). While there have been no reports of persistent slab avalanches since Dec 22, there have been recent reports of large whumpfs in the Hudson Bay, Hankin, and Babines area, suggesting that buried weak layers are still possible to human trigger.

Snowpack Summary

Strong wind is moving around 40-60 cm of snow that has fallen since New Year's Day. Reactive wind slabs can be found in exposed open terrain, while lower density snow can be found in sheltered terrain. In some parts of the region this snow could be sitting above a surface hoar layer and forming isolated persistent slabs on steep rolls in sheltered areas below treeline.

The lower snowpack has two crusts with potentially weak snow around them. Reports from the Smithers area suggest the upper crust is 60-90 cm below the surface and has shown signs of being possible to trigger from shallow areas. The other crust is near the bottom of the snowpack, and is most likely to trigger from steep, rocky slopes, with a shallow or thin to thick snowpack.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Be especially cautious near rock outcroppings, on steep convexities and anywhere the snowpack feels thinner than average.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

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.