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Avalanche Forecast

Archived

Dec 28th, 2023–Dec 29th, 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 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, Esplanade, Dogtooth, East Purcell, West Purcell.

A complex snowpack is making for challenging travel conditions in avalanche terrain. Exercise caution during this time of uncertainty.

Confidence

Moderate

Avalanche Summary

Several explosive-triggered small wind slabs were reported on Wednesday in alpine terrain in the northern Purcells. One of these avalanches stepped down to basal facets, producing a size 2 avalanche.

Snowpack Summary

A generally well-settled upper snowpack sits atop a particularly complex snowpack with several layers of note.

A layer of buried surface hoar is down roughly 50 to 70 cm and remains concerning in much of the region. It is less of a concern in areas where a strong, supportive crust exists above the surface hoar layer.

The lower snowpack is typically characterized by sugary, facetted crystals and a crust.

Snowpack depths at treeline average roughly 70-120 cm. However, there is significant variability in both snowpack structure and depths across the region.

Weather Summary

Thursday Night

Partly cloudy with no precipitation, southwest alpine winds 0 to 20 km/h, treeline temperature -5 °C.

Friday

Mostly sunny with no precipitation, south alpine winds 0 to 20 km/h, treeline temperature -3 °C.

Saturday

Mostly cloudy with no precipitation, south alpine winds 0 to 20 km/h, treeline temperature -3 °C.

Sunday

Mostly cloudy with trace amounts of snow, northwest alpine winds 0 to 20 km/h, treeline temperature -6 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • In times of uncertainty conservative terrain choices are our best defense.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

Problems

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.

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.