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Avalanche Forecast

Archived

Mar 28th, 2023–Mar 29th, 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.

Direct sun and rising freezing levels could weaken the snowpack on southerly aspects.

Wet loose avalanches may step-down into persistent weak layers and create large releases.

Approach shallow rocky areas with caution.

Confidence

Moderate

Avalanche Summary

We suspect that wet loose avalanches occurred Tuesday on south aspects throughout the region, as conditions were clear and sunny.

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 the weekend.

While activity may have started to taper off on the deeper layers, some locations in the region (especially thin, rocky areas in the alpine) are still of concern.

Snowpack Summary

In localized areas at upper elevations, convective flurries generated up to 15-20 cm of recent snow. This unconsolidated 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 are 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. Professionals are still tracking it to watch for signs of it waking up.

Weather Summary

The region will be under a building ridge of high pressure, with calm and dry conditions for the next few days.

Tuesday night

Clear with cloudy periods. Low alpine temperatures of -9 °C. Light easterly ridge wind. Freezing level at valley bottom.

Wednesday

Generally sunny. High alpine temperatures of -2 °C. Light easterly ridge wind. Freezing level rises to 2000 metres.

Thursday

Increasing cloudiness. High alpine temperatures of -3 °C. Light easterly ridge wind. Freezing level rises to 2000 metres.

Friday

Cloudy with sunny periods. Isolated flurries. High alpine temperatures of -3 °C. Light westerly ridge wind. Freezing level rises to 2000 metres.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid exposure to overhead avalanche terrain as temperatures increase.
  • If triggered loose wet avalanches may step down to deeper layers resulting in larger 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.