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Avalanche Forecast

Archived

Feb 24th, 2023–Feb 25th, 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 possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Purcells, Dogtooth, East Purcell, St. Mary.

Wind affected snow can be found at all elevations. Watch for dense, cohesive slabs in all areas - especially fresh slabs forming from southwest winds.

The weak snowpack continues to produce large slab avalanches. Keep your exploration to low angle supported terrain - avoiding thin, rocky and steep features.

Confidence

Moderate

Avalanche Summary

Natural and explosive triggered avalanches were reported on Tuesday and Wednesday to size 3, on all aspects and elevations. While natural activity appears to have tapered off, human-triggered slab avalanches remain possible while the recent storm snow begins to bond to underlying surfaces.

Deep persistent slab avalanches continue to be periodically reported throughout the region. Including a very large skier-triggered, fatal avalanche last Thursday.

This MIN post from Thursday observed a size 3 avalanche near Golden at least 1 m deep. Likely a naturally triggered slab, the failure plane is unknown. However this still indicates the weak and unpredictable snowpack remains concerning.

Snowpack Summary

Up to 50 cm of recent snow continues to be redistributed by wind. Winds have shifted from north/east to west currently. In sheltered areas loose snow can still be found. A layer of surface hoar is now buried by 30 to 50 cm in sheltered terrain and a thin sun crust on steep south-facing terrain. In general, the mid snowpack is well consolidated and bonding.

The lower snowpack contains a number of buried weak layers such as surface hoar with variable distribution, as well as a widespread layer of large, weak basal facets and depth hoar in places. These weaknesses have been responsible for a number of recent very large, destructive avalanches and will continue to be a concern.

Weather Summary

Friday Night

Mostly clear skies with no precipitation. Moderate westerly winds. Freezing levels below valley bottom.

Saturday

Snowfall begins, delivering 1-3 cm over the day. Freezing levels remain below valley bottom with alpine highs of -15 °C. Moderate southwest winds continue.

Sunday

Up to 5 cm overnight with snow continuing over Sunday with up to 5 cm possible throughout the day. Freezing levels around 600 m. Alpine high of -5 °C with moderate to strong southwest winds.

Monday

Cloudy with moderate southerly winds easing slightly. Alpine high of -9 °C. Freezing levels around 300 m. Possible flurries.

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.
  • Keep your guard up at lower elevations. Wind slab formation has been extensive.
  • Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.

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.