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Avalanche Forecast

Archived

Mar 24th, 2025–Mar 25th, 2025

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Purcells, Dogtooth, East Purcell.

Avalanche conditions will deteriorate over the next two days as temperatures rise. There is potential for large, destructive natural avalanches on buried weak layers to run far.

Confidence

Moderate

Avalanche Summary

On Friday and Saturday, natural wind slab avalanches up to size 2 were reported near Invermere, including one which stepped down to a persistent weak layer. Last week, numerous persistent slab avalanches were reported in the central Purcells, including remote triggers from 60 m away.

Looking forward, we can expect to see more large persistent slab avalanches over the next couple of days as temperatures spike.

Snowpack Summary

Recent snow may be wind affected at upper elevations while moist surfaces exist below 2000 m. Below, lies a complex snowpack.

An interface from early March, 30 to 50 cm deep, consists of a crust on sunny slopes and lower elevations, and surface hoar or facets in sheltered, shaded upper elevations.

Persistent weak layers from February and January, including crusts, facets, and surface hoar, are buried 50 to 100 cm deep and remain a concern.

The bottom of the snowpack is composed of large facets, which are becoming reactive again, with some very large avalanches recently failing on this layer.

Weather Summary

Monday night

Cloudy with a trace of snow. 10 to 20 km/h west ridgetop winds. Treeline temperature 0 °C. Freezing level 2000 m.

Tuesday

Cloudy with light rain. 10 to 20 km/h southwest ridgetop winds. Treeline temperature +4 °C. Freezing level rising to 2500 m.

Wednesday

Sunny. 10 to 20 km/h southeast ridgetop winds. Treeline temperature +6 °C. Freezing level rising to 3000 m.

Thursday

Cloudy with 3 to 8 cm of snow. 20 to 30 km/h southwest ridgetop winds. Treeline temperature 0 °C. Freezing level falling to 2000 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.
  • A moist or wet snow surface, pinwheeling, and natural avalanches are all indicators of a weakening snowpack.
  • Avoid exposure to overhead avalanche terrain; avalanches may run surprisingly far.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.