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Avalanche Forecast

Archived

Dec 26th, 2024–Dec 27th, 2024

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

Purcells, Crawford, Dogtooth, East Purcell, Moyie, St. Mary, West Purcell.

Rocky, wind-affected areas are a prime suspect for large, human-triggered avalanches.

Seek out sheltered, moderate-angled slopes for the best and safest riding.

Confidence

Moderate

Avalanche Summary

On Tuesday, a large skier-triggered avalanche (see this MIN) indicated reactive wind slabs failing on facets are a significant issue in alpine and treeline terrain.

On Wednesday, explosive control near Invermere produced numerous size 1 deep persistent slabs from steep, treeline terrain.

Both of these avalanche problems will continue into Friday. Steep, rocky, wind-loaded areas are prime suspects for either of these dangerous instabilities!

Snowpack Summary

5 to 20 cm of new snow has fallen in the past 24 hours. Accompanying southwest winds have likely redistributed this new snow, forming deeper deposits on leeward slopes at higher elevations.

A layer buried in early December is found roughly 20 to 90 cm below the surface. This layer varies, consisting of weak surface hoar or facetted crystals on shaded slopes and a sun crust with facets on south-facing slopes.

The base of the snowpack is made up of a thick crust and facets in many areas.

Weather Summary

Thursday Night

Cloudy with up to 5 cm of new snow. 15 to 40 km/h southwest ridgetop wind. Treeline temperature -5 °C.

Friday

A mix of sun and cloud with up to 3 cm of new snow. 10 to 30 km/h southwest ridgetop wind. Treeline temperature -6 °C.

Saturday

Cloudy with up to 10 cm of new snow. 25 to 50 km/h southwest ridgetop wind. Treeline temperature -4 °C.

Sunday

Mostly cloudy with up to 2 cm of new snow. 10 to 30 km/h southwest switching to northeast ridgetop wind. Treeline temperature -5 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid freshly wind-loaded features, especially near ridge crests, rollovers, and in steep terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.