Avalanche Forecast

Archived

Jan 10th, 2021–Jan 11th, 2021

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 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

Northwest Inland.

Extreme southwesterly winds will form fresh wind slabs in open terrain. Reactive wind slabs may be found much lower on slopes than what is typical.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system. Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

SUNDAY NIGHT: Snow; 5-10 cm. / Extreme, southwest ridgetop wind / alpine low temperature -7 / Freezing level 500 m.

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

TUESDAY: Flurries; 3-5 cm. / Light, southwest ridgetop wind / alpine high temperature -6 / Freezing level 500 m.

WEDNESDAY: Cloudy with isolated flurries; 0-3 cm. / Moderate, southwest ridgetop wind / alpine high temperature -7 / Freezing level 400 m.

Avalanche Summary

On Saturday, explosive control work near Ningunsaw produced several wind slabs to size 2.5 and one size 3 deep persistent slab failing on weak facets near the base of the snowpack. Another reminder of the "low probability; high consequence" scenario that persistent slab problems often create.

Additional snow and extreme winds are expected to form reactive wind slabs in open terrain.

Snowpack Summary

Strong to extreme winds are forming reactive wind slabs in exposed terrain at treeline and above. In the south of the region, a weak layer of surface hoar has been reported down 50-70 cm. in isolated sheltered areas.

The lower snowpack has two crusts with potentially weak snow around them. Reports from the Smithers area suggest the upper crust is 70-100 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.