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Avalanche Forecast

Archived

Mar 25th, 2023–Mar 26th, 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.

Inherently weak and dangerous snowpack structure remains.

High-consequence human-triggered avalanches are possible.

Keep avoiding steep, rocky, wind-affected terrain and choose small, low-consequence features.

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, strong solar radiation triggered several natural size 2 to 3 deep persistent slabs on south aspects, from rocky alpine and treeline features between 1900 and 2700 m. Additionally, a variety of solar-triggered loose wet avalanches up to size 2 were observed from steep, rocky slopes. A step-down avalanche, involving the mid-snowpack persistent weak layer, was also reported 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.

Saturday night

Cloudy with isolated flurries. Low alpine temperatures of -9 °C. Light northwest ridge wind up to 25 km/h. Freezing level at valley bottom.

Sunday

Cloudy with sunny periods. Isolated flurries. High alpine temperatures of -6 °C. Light easterly ridge wind. Freezing level rises to 1500 metres.

Monday

Cloudy with sunny periods. Isolated flurries. High alpine temperatures of -8 °C. Light westerly ridge wind. Freezing level rises to 1200 metres.

Tuesday

A mix of sun and clouds. High alpine temperatures of -5 °C. Light easterly ridge wind. Freezing level rises to 1600 metres.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
  • 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.