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Avalanche Forecast

Archived

Mar 19th, 2025–Mar 20th, 2025

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

Regions

Purcells, East Purcell, West Purcell.

Avoid steep, rocky, wind-affected terrain where triggering buried weak layers is most likely. Small avalanches in motion or cornice failures may also trigger these deeper layers.

Confidence

Moderate

Avalanche Summary

On Tuesday, a natural size 2 persistent slab was observed in the alpine which failed on a weak layer from mid-February down 70 cm. Explosives triggered two very large deep persistent slab avalanches in the Western Purcells, two persistent slab avalanches near Invermere which stepped down to deeper layers, and two storm slabs in the alpine.

On Monday, a naturally triggered size 3 persistent slab was reported on an east-facing alpine bowl near Invermere.

Snowpack Summary

30 - 50 cm of recent storm snow overlies a crust on sunny slopes and lower elevations, and surface hoar or facets on sheltered and shady upper elevations. Southwesterly wind formed slabs on lee features at treeline and above.

Several persistent weak layers consisting of a crust, facets, and/or surface hoar from February and January remain a concern. They are down 50 to 100 cm in most areas.

The bottom of the snowpack is composed of large facets in most areas. There is evidence that this layer is becoming reactive again, and some very large avalanches have failed on this layer recently.

Weather Summary

Wednesday Night

Partly cloudy with a chance of flurries. 5 to 15 km/h southwest ridgetop winds. Treeline temperature -10 °C. Freezing level valley bottom.

Thursday

Mostly cloudy with a chance of flurries. 10 to 20 km/h southwest ridgetop winds. Treeline temperature -3 °C. Freezing level 1600 m.

Friday

Mostly cloudy with light snowfall 3-6 cm. 20 to 30 km/h southwest ridgetop winds. Treeline temperature -2 °C. Freezing level 1700 m.

Saturday

A mix of sun and cloud. 15 to 25 km/h northwest ridgetop winds. Treeline temperature -3 °C. Freezing level 1600 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • 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.
  • Be aware of the potential for large, destructive avalanches due to deeply buried weak layers.

Problems

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.

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.

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.