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Avalanche Forecast

Archived

Feb 25th, 2023–Feb 26th, 2023

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
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.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells, Dogtooth, East Purcell, St. Mary.

Light snowfall will overly a wind affected snowpack, disguising recent wind slabs and building fresh ones. Take care around ridgelines and wind loaded features on all aspects.

The lower snowpack remains weak, small avalanches may easily step down to deeper layers. Keep a large margin of error by avoiding thin start zones and large slopes.

Confidence

Moderate

Avalanche Summary

Explosive control over the last 4 days has produced slab avalanches to size 3, including one deep persistent slab avalanche. Evidence of a natural cycle to size 3 continues to be observed. With the variable strong winds, activity was observed on all aspects and elevations.

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 over 1 m deep. Likely a naturally triggered slab, the exact failure plane is unknown. The continued activity indicates the weak and unpredictable snowpack remains concerning.

Snowpack Summary

Low density storm snow will sit over recent snowfall, redistributed by wind into wind slabs on all aspects.

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

Saturday Night

5 cm overnight, favoring the north. Freezing levels remain below valley bottom with alpine highs of -15 °C. Moderate southwest winds continue.

Sunday

Snow continuing over Sunday, 5 cm throughout the day. Freezing levels around 500 m. Alpine high of -7 °C with moderate southwest winds.

Monday

Cloudy with moderate southerly winds easing slightly. Alpine high of -9 °C. Freezing levels below valley bottom. Possible flurries.

Tuesday

A mix of sun and cloud with light southerly winds. Freezing levels below valley bottom, alpine high of -9 °C.

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.