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Avalanche Forecast

Archived

Mar 24th, 2023–Mar 25th, 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.

Danger ratings have declined but the inherently weak and dangerous snowpack structure remains.

A moderate rating reflects the possibility of large, high-consequence human-triggered avalanches. Remain diligent in your terrain selection by avoiding steep, rocky, wind-affected terrain and choosing small, low-consequence features.

Confidence

Moderate

Avalanche Summary

Near Panorama ski resort on Wednesday, a natural wind slab released from a southeast aspect in the alpine, stepping down to a mid-snowpack persistent weak layer at treeline elevation, resulting in a size 2 avalanche.

Earlier in the week, strong solar radiation triggered several natural size 2 to 3 deep persistent slabs on south aspects, reported 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.

Last Sunday, a remotely triggered size 2 persistent slab avalanche was reported on a NW aspect at 2400 m, failing down 70 cm on facets and triggered from 30 m away.

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, and wind-affected surfaces 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

Friday night

Cloudy with clear periods. Alpine temperatures drop to a low of -9 °C. Ridge wind southwest 10 to 30 km/h. Freezing level at valley bottom.

Saturday

A mix of sun and cloud with isolated flurries. Alpine temperatures reach a high of -6 °C. Ridge wind northwest 10-25 km/h. Freezing level rises to 1500 metres.

Sunday

Sunny with cloudy periods. Alpine temperatures reach a high of -7 °C. Ridge wind light from the east. Freezing level rises to 1500 metres.

Monday

Sunny with cloudy periods. Alpine temperatures reach a high of -8 °C. Ridge wind light from the west. Freezing level rises to 1200 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.
  • It's critical to stay disciplined and choose only well supported, low consequence lines.
  • 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.