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Avalanche Forecast

Archived

Mar 10th, 2023–Mar 11th, 2023

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.
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, West Purcell.

Diligently maintain a conservative mindset. You may not see signs of instability on the surface however the deep persistent weak layer remains a major concern at the bottom of the snowpack.

Avoid shallow, rocky, and wind-loaded terrain where triggering slab avalanches is most likely.

Confidence

Moderate

Avalanche Summary

On Thursday, a natural cornice failure triggered a size 2 persistent slab in the Dogtooth range north of Golden. This avalanche occurred on a northwest aspect in the alpine .

On Wednesday, two, size 3 cornice triggered avalanches were observed near Golden. The avalanches happened on northerly aspects and stepped down to the ground. Explosives control triggered a few avalanches on both the deep persistent weak layer to size 2 and on the persistent weak layer to size 3.

On Tuesday, a natural size 2.5 persistent slab avalanche was observed near Golden on a south aspect at 2600 m.

On March 1st, 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 5 cm of low-density new snow overlies hard, wind-affected surfaces in open areas, surface hoar and facetted snow in sheltered areas and a sun crust on steep solar slopes.

Buried surface hoar sits 50-70 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

Friday night

Cloudy with flurries, up to 5 cm of accumulation. Alpine temperatures drop to a low of -14 °C. Light northeast ridge wind. Freezing level at valley bottom.

Saturday

A mix of sun and cloud with isolated flurries. Alpine temperatures reach a high of -9 °C. Ridge wind light from the southwest. Freezing level rises to 700 meters.

Sunday

Sunny with cloudy periods and isolated flurries. Alpine temperatures reach a high of -6 °C. Light ridge wind from the southwest. Freezing level rises to 1000 meters.

Monday

Mainly cloudy with snowfall, trace to 15 cm of accumulation. Alpine temperatures reach a high of 1 °C. Ridge wind 30 to 60 km/h from the southwest Freezing level rises to 2000 meters.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Avoid areas with a thin or variable snowpack.
  • 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.

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.