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Avalanche Forecast

Archived

Dec 11th, 2023–Dec 12th, 2023

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

Regions

Kootenay Boundary, Bonnington, Grohman, Kootenay Pass, Norns, Rossland, Ymir, Crawford, Moyie, St. Mary, Kokanee, Retallack, Valhalla, Whatshan.

Start with small slopes, and watch for signs of instability like shooting cracks or whumpfs.

Investigate for crusts and buried weak layers that are good sliding surfaces for avalanches.

Confidence

Moderate

Avalanche Summary

On Saturday, some small (size 1) human triggered storm slab and loose dry avalanches were reported in the recent storm snow.

We're uncertain on whether avalanches could still release on the surface hoar layer described in the Snowpack Summary, so travel cautiously until there is evidence it is bonding or has been destroyed.

Snowpack Summary

30-55 cm of snow sits on a 5-15 cm melt-freeze crust. Below this crust you may find moist snow to ground, or dry, possibly refrozen snow and a layer of somewhat preserved surface hoar, ~60 cm deep.

Triggering this layer is most likely in areas where the overlying crust is thinner and less supportive, and where it didn't already fail in last weeks snow storm. We recommend treating this layer as suspect while we await more observations.

Snow depth is generally 70-110 cm at treeline, tapering quickly below. The mid and lower snowpack may contain a weak facet layer in shallower areas.

Weather Summary

Monday Night

Mostly clear. No new snow expected. Light north ridgetop wind. Treeline temperature around -5°C.

Tuesday

Sunny. No new snow expected. Light to moderate southwest ridgetop wind. Treeline temperature around -4°C.

Wednesday

Mostly sunny, increasing cloud in the afternoon. No new snow expected. Moderate to strong south ridgetop wind. Treeline temperature around -4°C, with possible temperature inversion in the alpine.

Thursday

Cloudy. 5-10 cm of snow expected. Moderate west ridgetop wind. Treeline temperature around -6°C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • Uncertainty is best managed through conservative terrain choices at this time.
  • Early season avalanches at any elevation have the potential to be particularly dangerous due to obstacles that are exposed or just below the surface.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.