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Avalanche Forecast

Archived

Mar 21st, 2023–Mar 22nd, 2023

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

Regions

Crowsnest North, Crowsnest South.

Watch for isolated pockets of wind slab at upper elevation. Avoid overhead exposure to cornices, especially during the heat of the afternoon.

This MIN post has us concerned that a deep persistent slab problem is developing in the region with the warm temperatures. Use extra caution in thin, rocky terrain where triggering a deep weak layer is most likely.

Confidence

Moderate

Avalanche Summary

On Sunday, a few natural size 1 loose wet avalanches were observed from steep terrain on solar aspects.

On Saturday, avalanches up to size 2.5 were reported in the Crowsnest South area which included some deep releases. This may be an indication that a deep persistent slab problem may be developing as warmer temperatures cause the upper snowpack to settle and form a slab over the weak layer at the base of the snowpack.

If you have any observations from this data sparse region, especially regarding a potential deep persistent slab problem, let us know what you are seeing by submitting a report to the Mountain Information Network.

Snowpack Summary

The snow surface consists of a sun crust on solar aspects, a rain crust below 1700 m, and wind-affected snow in exposed terrain at higher elevations. Small facets and/or surface hoar may also exist in shaded and wind-sheltered terrain.

A melt-freeze crust with facets above can be found 50 to 120 cm deep. The layer is currently dormant and has not produced any recent avalanche activity in the region but professionals are still tracking it to watch for signs of it waking up.

The weak layer at the base of the snowpack produced some large avalanches on the weekend and we are concerned that it might be becoming a more active problem with the current warm conditions. Caution is recommended in thin, rocky areas, mainly in the alpine but also possibly at treeline in some areas.

Weather Summary

Tuesday night

Clear. Alpine temperatures drop to a low of -7 °C. Light variable ridge wind. Freezing level at valley bottom.

Wednesday

Sunny. Alpine temperatures reach a high of 2 °C. Light variable ridge wind. Freezing level rises to 2200 metres.

Thursday

Sunny with cloudy periods. Alpine temperatures reach a high of -1 °C. Ridge wind southwest 15 to 40 km/h. Freezing level rises to 1900 metres.

Friday

A mix of sun and cloud with isolated flurries. Alpine temperatures reach a high of -5 °C. Ridge wind 10 to 40 km/h from the southwest. Freezing level at valley bottom.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
  • Cornice failures could trigger very large and destructive avalanches.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Problems

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.