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Avalanche Forecast

Archived

Mar 26th, 2023–Mar 27th, 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

Purcells, Dogtooth, East Purcell, West Purcell.

Be mindful that persistent instabilities are highly unpredictable and are still a concern.

It requires a patient and diligent mindset to keep avoiding steep, rocky, wind-affected terrain.

Confidence

Moderate

Avalanche Summary

Numerous natural dry loose avalanches (size 1) were observed within the recent snow on steep northerly alpine terrain in the south part of the region on Saturday.

Earlier in the week, several occurrences of very large deep persistent slabs (size 2.5 and 3) were observed on south aspects, from rocky alpine and treeline features between 1900 and 2700 m. These were triggered naturally by strong solar radiation, and some released to the ground. A natural step-down avalanche, involving the mid-snowpack persistent weak layer, was also reported on a south-facing slope near Panorama Ski Resort on Wednesday. A remotely triggered persistent slab avalanche was reported last Sunday, failing down 70 cm on facets and triggered from 30 m away on a NW alpine slope.

While recent activity may seem to have tapered off, remote and step-down avalanches are a reminder that the layers are likely still reactive in some locations in the region, especially thin, rocky areas in the alpine.

Snowpack Summary

At upper elevations, a dusting of new snow overlies a crust on solar aspects, faceted snow and surface hoar (up to 10 mm) in shaded and wind-sheltered areas. Wind-affected surfaces is also found in exposed areas.

In the middle of the snowpack, there are at least a couple of lingering persistent weak layers, including surface hoar in wind-sheltered terrain and a sun crust on south aspects. Activity on these layers has tapered off but still remains a concern in isolated areas.

The lower snowpack is made up of a widespread layer of large, weak facets and/or depth hoar crystals. This weak layer has been responsible for a number of recent very large, destructive avalanches and will likely continue to be a concern for the rest of the season.

Weather Summary

Unsettled weather will continue to bring scattered flurries until a ridge of high pressure invades the region early next week.

Sunday night

Cloudy with clear periods. Isolated flurries with trace accumulation. Low alpine temperatures of -6 °C. Light westerly ridge wind. Freezing level at valley bottom.

Monday

Cloudy. Isolated convective flurries. Local amounts up to 5 cm. High alpine temperatures of -6 °C. Light westerly ridge wind gusting 25 km/h. Freezing level rises to 1300 metres.

Tuesday

A mix of sun and clouds. High alpine temperatures of -5 °C. Light easterly ridge wind. Freezing level rises to 1400 metres.

Wednesday

Sunny with cloudy periods. High alpine temperatures of -3 °C. Light easterly ridge wind. Freezing level rises to 1800 metres.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
  • Conditions may have improved, but be mindful that deep instabilities are still present.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • Minimize your exposure time below cornices.

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.