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Avalanche Forecast

Archived

Jan 31st, 2023–Feb 1st, 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, human triggered possible.

Regions

Purcells, Dogtooth, East Purcell, West Purcell.

Exercise patience and maintain conservative terrain choices. Small wind slab avalanches have the potential to trigger larger avalanches deeper in the snowpack.

Find the newest blog here to learn more about managing this weak snowpack in the backcountry.

Confidence

Moderate

Avalanche Summary

On Monday, explosives control produced a few size 1 wind slabs.

On Sunday, explosives control produced several slab avalanches on all aspects of the alpine with results up to size 2. It also triggered a size 3 deep persistent slab avalanche that pulled to the ground on a west aspect.

On Saturday, a natural size 4 deep persistent slab avalanche was reported. The avalanche started as a wind slab in steep rocky terrain and stepped down to the ground. This avalanche was 80 to 200 cm deep and ran full path.

A skier remote size 1.5 wind slab avalanche was reported to have run on surface hoar below a wind slab. Numerous natural loose dry and wind slab avalanches were reported on all aspects of the alpine.

Snowpack Summary

5 to 10 cm of accumulated new snow will further build wind slabs in exposed areas at the treeline and above. These new wind slabs have developed on a variety of surfaces including previously wind-affected surfaces, a small layer of surface hoar, and a sun crust.

The mid-snowpack contains a couple of weak layers. 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 60 cm down. The surface hoar is most prevalent in sheltered areas while crusts with faceted snow are more widespread.

The bottom of the snowpack is weak, faceted and contains a weak layer from late November. Snowpack depths range between 80 and 180 cm at treeline and are shallowest in the eastern part of our region.

Weather Summary

Tuesday Night

Mainly cloudy with isolated flurries, 3 to 5 cm. Winds 20 to 30 km/h west, Treeline temperatures -15 °C.

Wednesday

Mainly cloudy, with 5 to 10 cm of new snow. Winds 20 to 30 km/h, treeline temperatures of -12 °C.

Thursday

Mainly cloudy, trace accumulations. 10 to 20 km/h southwest winds. Treeline temperatures -10 °C.

Friday

Increasing clouds, 2 to 5 cm of new snow, 10 to 20 km/h southwest winds, Treeline temperatures -9 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Approach lee and cross-loaded slopes with caution.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • Uncertainty is best managed through conservative terrain choices at this time.

Problems

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.

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.