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Avalanche Forecast

Archived

Dec 25th, 2024–Dec 26th, 2024

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

Regions

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

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

Confidence

Moderate

Avalanche Summary

On Tuesday, several skier-triggered wind slabs were reported from alpine and treeline terrain. In the Invermere area, several skier-triggered deep persistent slabs (size 1) were reported from NW-NE aspects at treeline and below. A few natural (size 1-2) wind slabs were also reported from alpine terrain.

Looking forward to Wednesday, fresh reactive wind slabs are expected to form in lee areas throughout the day as southwest wind redistributes new snow.

Snowpack Summary

Up to 15 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 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. The only location where this basal layer has shown signs of instability is in the Invermere area.

Weather Summary

Wednesday Night

Mostly cloudy with up to 3 cm of new snow. 15 to 40 km/h southwest ridgetop wind. Treeline temperature -8 °C.

Thursday

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

Friday

A mix of sun and cloud with isolated flurries. 15 to 30 km/h southwest ridgetop wind. Treeline temperature -7 °C.

Saturday

Cloudy with up to 10 cm of new snow. 30 to 60 km/h southwest wind. Treeline temperature -3 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be careful as you transition into wind-affected terrain.
  • Avoid steep, rocky, and wind-affected areas where triggering slabs is more likely.
  • 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.