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

Regions

North Rockies, Kakwa, McGregor, Pine Pass, Tumbler.

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.

Recent observations suggest the deep persistent slab problem has been active in recent days. Keep this in mind as travel through terrain, especially in shallow snowpack areas in the north and east of the region.

Confidence

Moderate

Avalanche Summary

In the past few days, several natural and human-triggered wind slabs have been observed from a variety of aspects in alpine terrain and treeline terrain as northerly winds impacted the region. Check out this MIN from Pine Pass on Saturday for an example.

Another MIN report from Pine Pass on Sunday shows a very large deep persistent slab from alpine terrain that was likely triggered by a cornice failure or wind-loading. This is the first observation in several weeks of deep persistent slab activity and is an indication that this layer should be on our radar, particularly in the shallower snowpack areas in the region.

Snowpack Summary

Shifting winds have redistributed recent storm snow into wind slabs on a variety of aspects while soft snow remains in sheltered areas. Storm snow overlies heavily wind-affected snow.

The middle of the snowpack is generally strong.

A weak layer of large and weak facets is found near the base of the snowpack. This layer is of greatest concern in shallow snowpack areas in the north and east of the region.

Weather Summary

Monday night

Clear with cloudy periods. Alpine temperatures drop to a low of -10 °C. Ridge wind southeast 10-25 km/h. Freezing level at valley bottom.

Tuesday

A mix of sun and cloud with flurries. Alpine temperatures reach a high of -12 °C. Ridge wind south 25-40 km/h. Freezing level at valley bottom.

Wednesday

Sun and cloud with isolated flurries. Alpine temperatures reach a high of -13 °C. Ridge wind southeast 30-50 km/h. Freezing level at valley bottom.

Thursday

Sunny. Alpine temperatures reach a high of -6 °C. Ridge wind light from the southeast. Freezing level at valley bottom.

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.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • 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.

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.