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Avalanche Forecast

Archived

Dec 6th, 2022–Dec 7th, 2022

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

Regions

Kootenay Boundary, Bonnington, Grohman, Kootenay Pass, Norns, Rossland, Ymir, Moyie, St. Mary.

Conditions are more complicated than what meets the eye. Fresh wind slabs formed at upper elevations. Riders may be drawn to more sheltered areas around treeline to avoid these wind slabs, but should consider that this is where the persistent slab problem has been most problematic to date. Keep your terrain choices conservative and don't let good riding lure you into steeper terrain.

Confidence

Low

Avalanche Summary

A layer of surface hoar from mid-November buried 40-80 cm deep continues to be reactive. Widespread whumpfing and cracking continue to be reported, with the most reactivity observed in sheltered and shaded areas at treeline.

On Friday, a remotely triggered natural avalanche was reported on a steep east-facing feature near Kootenay Pass, likely failing on this layer. Read the MIN report here.

Thank you for all the great MIN reports! They are extremely helpful to us in the early season when snowpack information is limited. Keep them coming!

Snowpack Summary

Up to 20 cm new low-density snow was redistributed by westerly wind that formed fresh wind slabs in the alpine and at treeline. In sheltered terrain, cold temperatures likely maintained low-density, powdery snow.

On south-facing aspects, a crust may be found below the new snow from solar radiation and warm temperatures on Sunday.

There are two prominent weak layers in the upper snowpack. A weak layer of surface hoar can be found 30-60 cm down. Another weak interface that was formed during the dry period in mid-November is buried 60-90 cm deep. This layer consists of sugary faceted grains, large surface hoar crystals in sheltered terrain features, and a crust on steep sun-exposed slopes. Reports of whumpfing, cracking, and recent avalanches suggest these interfaces are not bonding well.

We have limited information at this point in the season, we're hoping to gain more information on the distribution and sensitivity of these layers as we collect more field observations.

Snowpack depths average 80-160 cm in the alpine. Below treeline elevations are now above the threshold for avalanches in many areas.

Weather Summary

Tuesday night

Mostly cloudy with a trace of new snow. Westerly wind 30 km/h at ridgetop. Treeline temperature low -11 °C.

Wednesday

Mostly cloudy with a trace of new snow. Westerly wind 20-30 km/h at ridgetop. Treeline temperatures reach a daytime high of -8 °C.

Thursday

Sunny periods but mostly cloudy with snowfall, up to 10 cm of accumulation is possible. Southwesterly wind 30-50 km/h at ridgetop. Treeline temperatures reach a daytime high of -6 C.

Friday

Mostly cloudy with isolated flurries, up to 5 cm of accumulation is possible. Southwest wind 20 km/h at ridgetop. Treeline temperature high -6 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Remote triggering is a concern, watch out for adjacent and overhead slopes.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

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.