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Avalanche Forecast

Archived

Feb 12th, 2023–Feb 13th, 2023

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

Regions

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

The message remains the same – a complex, and generally weak snowpack is best managed by sticking to lower angled, low consequence terrain. Large persistent slab or deep persistent slab avalanches are reported every two or three days.

Confidence

Moderate

Avalanche Summary

Over the past week there have been continual reports of large persistent and deep persistent slab avalanches across the Purcells. Here are some recent examples that illustrate the currently dangerous snowpack conditions:

  • On Saturday, skiers at Quartz Creek remotely-triggered a size 3 avalanche on a northwest-facing alpine slope at 2300 m. It failed on a 40 to 80 cm deep weak layer.

  • On Friday, skiers near Invermere remotely-triggered a size 2 on a north aspect at 2400 m. The avalanche started on a 30 cm deep surface hoar layer and stepped down to the deep persistent weak layer.

  • On Thursday, skiers near Kimberlely reported several very large persistent slab avalanches, including a size 3 avalanche that was remotely-triggered on a treeline feature.

Smaller size 1 to 2 wind slab avalanches have also been reported in alpine terrain over the past few days.

Snowpack Summary

30 to 60 cm of snow since late January is settling and being redistributed by southwest wind. A weak layer of surface hoar or facets and crust is buried beneath that snow, and has become reactive in the southern and western parts of the Purcells where it is more deeply buried (e.g., along Kootenay Lake and the St. Mary drainage). A layer from late November is found 75 to 150 cm deep throughout the Purcells and is part of a generally weak, faceted lower snowpack. Snowpack depths range between 90 and 200 cm at treeline, with the shallowest depths found on the eastern edge of the Purcells.

Weather Summary

Sunday night

Cold front crossing the Purcells overnight, 5 to 15 cm of snow, 50 to 80 km/h southwest wind, treeline temperatures around -6 ºC.

Monday

Mostly cloudy with convective flurries bringing up to 5 cm of snow, 40 km/h southwest wind, treeline temperatures around -4 °C.

Tuesday

Sunny with a few clouds, no significant precipitation, 20 km/h north wind, treeline temperatures drop to -10 °C.

Wednesday

Mix of sun and cloud, no precipitation, 30 km/h northwest wind, treeline temperatures around -8 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • It's critical to stay disciplined and choose only well supported, low consequence lines.
  • Use careful route-finding and stick to moderate slope angles with low consequences.
  • Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
  • Avoid steep convex slopes.
  • Be especially cautious as you transition into wind affected terrain.

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.