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Avalanche Forecast

Archived

Jan 13th, 2021–Jan 14th, 2021

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

Regions

Northwest Inland.

Strong to extreme southwest winds are likely forming fresh and reactive wind slabs. Seek out sheltered, low-angle slopes and watch for reactive pockets around steep rolls and ridge features.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

WEDNESDAY NIGHT - Cloudy with clear periods and isolated flurries / southwest wind, 20-30 km/h / alpine low temperature near -10 

THURSDAY - Mainly cloudy with a few flurries / southeast wind, 60-80 km/h / alpine high temperature near -3

FRIDAY - Cloudy with flurries, 3-5 cm / southwest wind, 50-70 km/h / alpine high temperature near -4 

SATURDAY - Cloudy with flurries, 3-5 cm / southwest wind, 30-60 km/h / alpine high temperature near -5

Avalanche Summary

Wind slabs may continue be reactive to human triggers on Thursday, especially at upper elevations. 

There was a report of a natural avalanche cycle up to size 2 from wind loaded terrain in the south of the region on Tuesday.

There were a few explosives triggered size 2 avalanches reported near the southern boundary of the region on Sunday.

On Saturday, explosive control work near Ningunsaw (just outside the region) 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.

Snowpack Summary

A few cm of recent fresh snow is likely sitting on widespread wind slabs in open terrain in the alpine and at treeline. These wind slabs may sit on a weak layer of surface hoar that was recently buried at treeline and below treeline.

In the south of the region, another weak layer of surface hoar that was buried around the New Year has been reported down 50-70 cm in sheltered areas.

The lower snowpack has two crusts with potentially weak, faceted snow around them. Reports from the Smithers area suggest the upper crust is 70-140 cm below the surface and has shown signs of being possible to trigger from shallow areas. The deeper 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

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Be especially cautious near rock outcroppings, on steep convexities and anywhere the snowpack feels thinner than average.

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.