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Avalanche Forecast

Archived

Feb 11th, 2023–Feb 12th, 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.

The most recent reports include a remotely triggered size 2 avalanche near Invermere on Friday, that occurred 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. Another size 2 remote-triggered avalanche occurred on a southeast aspect at 2250 m near Golden. On Thursday, several very large persistent slab avalanches were observed west of Kimberley, including some that were remotely triggered by skiers.

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

Snowpack Summary

20 to 60 cm of snow since late January is gradually settling and in open terrain has been redistributed by west and southwest wind. A weak layer of surface hoar, facets and crusts 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

Saturday night

Partly cloudy, no precipitation, 30 to 40 km/h west wind, treeline temperatures drop to -10 ºC.

Sunday

Sunny periods in the morning then increasing cloud in the afternoon, isolated flurries with trace amounts of snow, 40 to 50 km/h southwest wind, treeline temperatures to -5 °C with freezing level climbing to 1200 m.

Monday

Flurries with 5 to 10 cm of new snow, 40 to 60 km/h southwest wind, treeline temperatures reach -3 °C.

Tuesday

Mix of sun and cloud, no significant precipitation, 20 km/h north wind, treeline temperatures drop to -10 °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.

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.

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.