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Avalanche Forecast

Archived

Mar 6th, 2023–Mar 7th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

North Columbia, South Columbia, Esplanade, Jordan, North Selkirk, Shuswap, West Purcell, Badshot-Battle, Central Selkirk, Goat, Gold, Kokanee, North Okanagan, Retallack, Valhalla, Whatshan.

Don't let good visibility lure you into dangerous terrain. Wind slabs may exist on a variety of aspects due to recently shifting wind direction. The air is cold but the March sun can be strong so avoid exposure to cornices and watch for signs of warming on steep south aspects. Thin rocky areas will remain a concern for triggering deeply buried weak layers in this complex snowpack.

Confidence

Moderate

Avalanche Summary

During the storm last week, a natural avalanche cycle occurred with storm slabs reported up to size 3.5.

In the past few days, strong solar input has initiated loose dry avalanches from steep solar aspects and cornice failures up to size 2.5, with some of these cornices pulling slabs on the slope below. Several human-triggered storm and wind slabs have been reported on all aspects in steep and unsupported or wind-loaded features in the alpine and treeline.

Explosive control on Saturday and Sunday produced numerous large persistent and deep persistent slabs up to size 4 on a variety of aspects in the alpine. Several large cornices were also initiated with explosives.

Two notable deep persistent slab avalanches occurred on Saturday, both in shallower snowpack areas in the eastern part of the region. One was a size 3 natural that occurred on an east aspect in the alpine. This avalanche occurred on a re-loaded bed surface. The other was a size 3.5 skier-remote avalanche on a shallow, south-facing alpine slope. These avalanches highlight the terrain we are most concerned about triggering deep persistent slabs: shallow, thick-to-thin alpine and upper treeline terrain.

Read more about managing the deep persistent slab problem in our latest Forecaster Blog.

Snowpack Summary

On the surface, a sun crust can be found on steep south-facing aspects and surface hoar growth has been reported in some parts of the region. Last week's 20-60 cm of storm snow has been redistributed by variable winds in exposed areas creating pockets of wind slab that may be found on all aspects.

This recent storm snow overlies a weak layer of faceted snow and a sun crust on sun-affected slopes. This layer has been noted as a failure plane for some recent avalanche activity, as seen in this MIN report from Saturday. The remainder of the mid-snowpack is generally strong.

The November facets are still prominent at the base of the snowpack. They are showing signs of rounding but there is still a considerable step in resistance between them and the overlying snow. These facets are most pronounced in shallow rocky areas.

Weather Summary

Monday night

Clear periods. Alpine temperatures drop to a low of -10 °C. Light southeasterly ridge wind. Freezing level at valley bottom.

Tuesday

Sunny with cloudy periods. Alpine temperatures reach a high of -7 °C. Ridge wind southeast 10-25 km/h. Freezing level 500-900 metres.

Wednesday

Mainly sunny. Alpine temperatures reach a high of -6 °C. Ridge wind light from the southeast. Freezing level 700-1100 metres.

Thursday

Sunny with cloudy periods. Alpine temperatures reach a high of -8 °C. Ridge wind light from the southeast. Freezing level 800 metres.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

Problems

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.

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.