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Avalanche Forecast

Archived

Dec 25th, 2024–Dec 26th, 2024

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

Regions

Kootenay Boundary, Bonnington, Grohman, Kootenay Pass, Norns, Rossland, Ymir.

Building storm slabs in combination with buried weak layers necessitates good travel habits and lower-consequence terrain choices.

Confidence

Moderate

Avalanche Summary

On Tuesday, several skier-triggered storm slabs (size 1) were reported in the Kootenay Pass and Whitewater area. One natural storm slab was reported near Whitewater (size 2). Several skier-triggered persistent slabs (size 1) were reported in the Bonnigtons-MIN.

Looking forward to Thursday, storm slabs are expected to build throughout the day with new snow and wind. Remember that buried weak layers remain a concern, and could become more reactive with increased load.

Snowpack Summary

Up to 30 cm of new snow can be expected by end of day Thursday. Southwest winds will redistribute this new snow, forming deeper deposits on leeward slopes at higher elevations. A crust is present near the surface at lower elevations, with moist snow likely near the valley bottom where precipitation falls as rain.

The upper snowpack continues to settle and bond well following significant snowfall over the last two weeks.

Weak layers of surface hoar or facets and a crust may persist in the mid-snowpack, and snowpack tests continue to indicate potential instability.

The lower snowpack is generally strong and well-bonded.

Weather Summary

Wednesday Night

Cloudy with up to 10 cm of new snow. 30 to 50 km/h southwest ridgetop wind. Treeline temperature -6 °C.

Thursday

Cloudy with up to 10 to 20 cm of new snow. 30 to 50 km/h southwest ridgetop wind. Treeline temperature -5 °C.

Friday

A mix of sun and cloud with up to 5 cm of new snow. 15 to 30 km/h southwest ridgetop wind. Treeline temperature -5 °C.

Saturday

Cloudy with up to 20 cm of new snow. 30 to 60 km/h southwest wind. Treeline temperature -4 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • As the storm slab problem worsens, the easy solution is to choose more conservative terrain.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.

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.