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Avalanche Forecast

Archived

Mar 8th, 2023–Mar 9th, 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 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, Esplanade, Dogtooth, East Purcell, West Purcell.

The snowpack remains weak, requiring users to carefully select conservative terrain for a safe day. Avoid shallow rocky terrain where the snowpack transitions from thick to thin and you are more likely to trigger a large destructive deep persistent slab avalanche.

Confidence

Moderate

Avalanche Summary

On Tuesday, a natural size 2.5 persistent slab avalanche was observed near Golden on a south aspect at 2600 m. Explosives control triggered a few persistent slabs to size 2 and wind slabs to size 1.

On Monday, several cornice triggered persistent slab avalanches were reported to size 3 throughout the region.

Last Wednesday a fatal avalanche incident involving a group of skiers occurred in the Purcell Mountains west of Invermere BC. The size three avalanche was triggered on a southwest facing slope at 2500 m. The weak layer of facets buried in late November that sits at the bottom of the snowpack was responsible for this avalanche.

Snowpack Summary

Up to 40 cm of storm snow from earlier in the week sits over wind affected surfaces. Wind slabs may be found on all aspects due to variable winds in the past few days. A melt-freeze crust covers the surface of steep solar slopes

Buried surface hoar sits 30-60 cm deep in sheltered terrain features, and a thin sun crust exists at the same depth on steep south-facing terrain. Several other layers from January can also be found in the top 100cm of the snowpack.

The lower snowpack is made up of a widespread layer of large, weak basal facets and depth hoar in some areas. this weakness has been responsible for a number of recent very large, destructive avalanches and will continue to be a concern.

Weather Summary

Wednesday Night

Clear skies. Easterly winds 15-25 km/h. Treeline temperatures, high of -12.

Thursday

Mainly sunny with scattered clouds in the afternoon. Southerly winds 10-20 km/h. Treeline temperatures, high of -10.

Friday

Partly cloudy and isolated flurries, 2-7 cm accumulation. East winds 10-25 km/h. Treeline temperatures, high of -10.

Overnight flurries continue 1-5 cm accumulation. Winds switch to the southwest 25-40 km/h.

Saturday

A mix of sun and cloud with isolated flurries, 2-3 cm accumulation. Southwest winds 10-25 km/h. Treeline temperatures, high of -8.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid areas with a thin or variable snowpack.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • Remote triggering is a concern, watch out for adjacent and overhead slopes.

Problems

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.

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.