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Avalanche Forecast

Archived

Jan 22nd, 2023–Jan 23rd, 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, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells, Dogtooth, East Purcell, West Purcell.

Continue to use conservative terrain choices and have a 'plan B' to avoid getting surprised.

Be aware that weak layers buried further down in the snow pack are still a factor.

Confidence

Moderate

Avalanche Summary

Much of Saturday's avalanche activity was focused in West Purcell. These avalanches were caused by a mix of storm slab, wind slab, and cornice fall. They have been triggered accidentally and with the use of explosives.

An avalanche of note was a size 2 that a skier triggered accidentally. This avalanche was of note because it was from our persistent slab problem, buried surface hoar and because it happened on such a low angle. Our persistent slab problem and deep persistent slab problem are still problems.

Snowpack Summary

Surface hoar growth has developed into the alpine. Wind slabs can be found in exposed areas. The top 20 of snow may contain a surface hoar or rain crust layer depending on elevation and location within the region.

Buried layers that are presently a concern are as follows. The first is down 30 to 50 cm and is a layer of surface hoar from early January. The second is a layer of surface hoar, facets, and crust created in December and found 40 to 90 cm down. The surface hoar is most prevalent in sheltered areas while crusts and any associated faceted snow are more widespread.

The bottom of the snowpack contains yet more weak, faceted snow. The total depth of this weak and shallow snowpack ranges between 80 and 180 cm at treeline and can be found at its most shallow in the eastern part of our region.

Weather Summary

Sunday Night

Mostly clear, possible trace accumulation, 15 to 25 km/h west winds, treeline temperatures of -9 C.

Monday

A mix of sun and cloud, trace accumulation, 20 to 30 km/h west wind, treeline temperatures -10 to -6 C.

Tuesday

A mix of sun and cloud, no accumulation, 25 km/h west northwest wind, treeline temperatures -9 C.

Wednesday

Cloudy with sunny breaks, no accumulation, 20 to 30 km/h northwest wind, treeline temperatures -10 C.

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.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.

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.