Avalanche Forecast

Archived

Dec 12th, 2022–Dec 13th, 2022

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 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.

Regions

Purcells, Dogtooth, East Purcell.

Buried weak layers and wind slabs are your main concern today.

Considered your up track and ski down accordingly. Check out our latest blog for advice on how to manage this problem.

Be on the lookout for whumpfing and shooting cracks.

Confidence

Moderate

Avalanche Summary

On Saturday there was a report of a skier triggering a size 2, large, avalanche. This was at treeline and on a north-facing slope. It failed on the buried weak layer and in some places was 45 cm deep. Local operators using explosives also triggered this layer and wind slabs producing several avalanches up to size 2 as well.

Snowpack Summary

About 10 to 20 cm of lighter snow sits on a variety of surfaces. In many places in the alpine it sits on stubborn windslabs. In sheltered areas it sits on more consolidated snow, ranging in 5 to 15 cm. Beneath that is a buried layer of surface hoar sits 20 to 45 cm deep and remains a layer of concern. On Saturday we received reports of several large avalanches failing on this layer. They were triggered intentionally through the use of explosives and accidentally by skiers.

Generally speaking, we have a thin snowpack. The bottom of the snowpack near the ground is very weak due to faceting.

The overall height of snow is highly variable throughout the region with around 40 to 140 cm in the alpine.

Weather Summary

Monday Night

Clear with cloudy periods, trace accumulation, winds northwest 10 km/h, temperature -5 C at 1500 m due to a temperature inversion.

Tuesday

A mix of sun and cloud, no accumulation, winds northwest 10 km/h, temperature -6 C at 1500 m due to a temperature inversion.

Wednesday

A mix of sun and cloud, trace accumulation, winds northwest 15 km/h, temperature -10 C at 1500 m.

Thursday

Sunny with cloudy periods, no accumulation, winds northwest 10 to 20 km/h, temperature -10 C at 1500 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Be especially cautious as you transition into wind affected terrain.
Caution around convexities or sharp changes in terrain.

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.

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.